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Allogeneic stem-cell transplant (allo-Stem-cell transplantation) is the only potentially curative therapy for chronic myelogenous leukemia (chronic myelogenous leukemia). This aggressive approach is appropriate only for young (less than 55 years of age), fit patients with matched donors — a profile that accounts for less than one-third of the chronic myelogenous leukemia population.

Since its launch in 2001, the tyrosine kinase inhibitor imatinib (Novartis’s Gleevec/Glivec), alone or in combination with other agents, has been regarded as the treatment of choice for patients not destined for immediate allo-Stem-cell transplantation. Previously, the standard treatment for patients with newly diagnosed chronic-phase chronic myelogenous leukemia who were ineligible for allo-Stem-cell transplantation was interferon-alpha (interferon-a), either alone or in combination with low-dose cytarabine (LDAC) (Pfizer’s Cytosar-U, generics). interferon-a largely replaced hydroxyurea (Bristol-Myers Squibb’s Hydrea, generics) in the mid-1990s, when clinical trials demonstrated that it induces major cytogenetic responses in about one-third of patients and achieves an overall survival advantage of one to two years compared with hydroxyurea.

When disease progresses to the accelerated and blastic phases, more aggressive chemotherapeutic regimens may be employed (e.g., an anthracycline and cytarabine, high-dose cytarabine alone). In select cases, autologous transplantation is attempted. However, once chronic myelogenous leukemia starts to progress, no treatment is particularly effective. Purely palliative interventions include radiotherapy, splenectomy, and leukapheresis (the mechanical removal of white blood cells).

With the exception of the purely palliative interventions, which we do not discuss further in this report, the agents and procedures employed in the treatment of chronic myelogenous leukemia are described in the following sections. TABLE:Current Therapies Used for Chronic Myelogenous Leukemia lists brand names, marketing companies, dosage, and market availability of agents commonly used in the treatment of chronic myelogenous leukemia. TABLE:Current Therapies Used for Chronic Myelogenous Leukemia illustrates the achievements of current treatment modalities in various patient populations.

Because of the long median survival of patients in chronic-phase chronic myelogenous leukemia, primary endpoints in studies involving these patients are often hematologic and cytogenetic response rates. These response rates act as an indicator of length of survival. As novel drugs are achieving complete hematologic and complete cytogenetic responses, molecular response is becoming an increasingly popular trial end point owing to the fact that a complete molecular response indicates disease eradication. The following types of responses are generally measured:

TABLE. Current Therapies Used for Chronic Myelogenous Leukemia

Agent	Company/Brand	Daily Dose	Availability
Protein tyrosine kinase inhibitors
Imatinib	Novartis’s Gleevec, Glivec	400 mg	US ,France, Germany, Italy, Spain, UK, Japan
Interferons
lnterferon-alpha-2a	Roche’s Roferon-A	5x 106lU/m2	US ,France, Germany, Italy, Spain, UK, Japan
lnterferon-alpha-2b	Schering-Plough’s Intron-A	5x 106lU/m2	US ,France, Germany, Italy, Spain, UK, Japan
lnterferon-alpha-N1	Sigma -Tau’s Humoferon, GlaxoSmithKline’s Wellferon, Sumitomo’s Sumiferon	5x 106IU /m2	Italy, Spain, Japan
Interferon-alpha	Janssen-Cilag’s Cilferon-a, Otsuka’s Oif	5x 106IU /m2	Italy, Japan
Cytotoxic agents
Cytarabine	Pfizer’s Cytosar-U, generics	20 mg/m2	US ,France, Germany, Italy, Spain, UK, Japan
Hydroxyurea	Bristol-Myers Squibb’s Hydrea, generics	40-50 mg/kg	US ,France, Germany, Italy, Spain, UK, Japan
Busulfana	GlaxoSmithKline’s Myleran	0.1 mg/kgb	US ,France, Germany, Italy, Spain, UK, Japan

^aBusulfan is now rarely used in the treatment of chronic myelogenous leukemia but is included in the table for historical reasons. ^bWhen used in myeloablative regimens prior to allogeneic progenitor stem-cell transplantation, a dose of 8-16 mg/kg is given over four days.

TABLE. Achievements of Current Therapies Used for CML, 2005: Benchmarks for Evaluation of Emerging Therapies

Setting	Treatment	Four-Year Survival/ Ten-Year Survival (%)	CHR(%)	cytogenetic response(%)	PFS After 18 Months/ 42 Months (%)	Median Survival (months)
Late chronic-phase chronic myelogenous leukemia after failure with interferon-a therapy	Imatinib 400 mg dailya		95	41	89/—	—
Early chronic-phase chronic myelogenous leukemia	Imatinib 400 mg dailyb	—	97	76	97/90c	—
Early chronic-phase chronic myelogenous leukemia	interferon-a 5 MIU/m2 dailyd	—	80	26e	—	89
Chronic phase-chronic myelogenous leukemia	interferon-a 9 MIU/m2 dailyf	—/47g	—	10	—	104g
Early chronic-phase chronic myelogenous leukemia	interferon-a + LDAC (10 mg)h	70/—	92	50	—	—

A 42-month follow-up showed PFS of 90% for patients who had achieved cytogenetic response within 12 months of beginning therapy. For patients not achieving cytogenetic response, PFS was 75%.

^dKantarjian HM, 1996.

^e Five-year survival for patients who achieved cytogenetic response was 90%.

^fThe Italian Cooperative Study Group, 1998.

9 Data for Sokal’s low-risk patients.

^hKantarjian HM, 1999.

cytogenetic response = Complete cytogenetic response.

CHR = Complete hematologic response.

CML= Chronic myelogenous leukemia.

INF-α =interferon-a

LDAC = Low-dose cytarabine.

PFS = Progression-free survival.

•  Hematologic response. A complete hematologic response (CHR) is the absence of disease-related symptoms and splenic enlargement, normalization of the white blood cell count (i.e., a count between 4,000 and 11,000 per mm³), and a normal differential white blood cell and platelet count. If only some of these criteria are met, the response may be classed as partial.

•  Cytogenetic response. A complete cytogenetic response is the absence of detectable Ph-positive cells (cells expressing the Philadelphia chromosome) in metaphase. If a percentage of Ph-positive cells is detectable, the response may be classed as a major cytogenetic response (or partial cytogenetic response) (1-34% Ph-positive cells); minor cytogenetic response (35-94% Ph-positive cells); or no cytogenetic response (95-100% Ph-positive cells). Cytogenetic responses are clinically important because they are associated with better prognosis.

• Molecular response. A molecular response is the disappearance or reduction in quantities of BCR-ABL transcripts (i.e., amount of BCR-ABL oncoprotein). Monitoring the level of BCR-ABL is a way of predicting long-term patient outcomes. A thousandfold (>3 log) reduction in levels of BCR-ABL is defined as a major molecular response. The authors of a study (involving more than 1,000 chronic myelogenous leukemia patients) estimated that 100% of chronic myelogenous leukemia patients who have achieved a cytogenetic response and who achieve a major molecular response at 12 months will remain progression-free after another year. A complete molecular response is when there is no evidence of BCR-ABL transcripts, indicating disease eradication. The levels of BCR-ABL transcripts are usually measured by a quantitative real-time polymerase chain reaction (PCR) assay.

Pathophysiology

Leukemias are cancers of the hematopoietic (blood-producing) system. The word leukemia derives from the Latin word for white blood and refers to the proliferation of white blood cells (leukocytes) in people with this disease.

FIGURE. The hematopoietic cascade: development of mature blood cells from pluripotent stem cells.

Mature blood cells (red cells, white cells, and platelets) are normally produced in the bone marrow from primitive hematopoietic stem cells. (FIGURE. The hematopoietic cascade: development of mature blood cells from pluripotent stem cells shows the different lineages of blood cells and the stages involved in their maturation.) The blood cells mature and differentiate through a sequence of steps involving a series of complex — and incompletely understood — interactions with growth factors, cytokines, and other cells in the bone marrow. Once mature, the blood cells leave the bone marrow and enter the general circulation, where they have a limited life span.

Leukemia occurs when a genetic mutation arises in a single cell that interferes with the normal maturation and differentiation of developing leukocytes. These changes produce “immortal” white blood cells, in which the mechanisms of programmed cell death (apoptosis) are inactivated. The white blood cells proliferate without limitation, eventually replacing normal bone marrow cells and entering the peripheral bloodstream.

Unlike acute leukemias (which have a sudden onset, progress rapidly, and, if untreated, can be fatal in as little as two months from the onset of symptoms), chronic leukemias are indolent. They have an insidious onset, progress slowly, and can remain asymptomatic and require no treatment for months or years.

Leukemia is a heterogeneous disease; in other words, the leukemic mutations may affect any stage of hematopoietic differentiation, and the type of leukemia can be characterized by the type of affected cell. If the mutations affect the maturation of lymphoid cells, lymphoid leukemias result (e.g., chronic lymphocytic leukemia, acute lymphocytic leukemia); maturation arrest in myeloid differentiation results in myeloid leukemias (e.g., chronic myelogenous leukemia, acute myelogenous leukemia).

In chronic myelogenous leukemia, maturation arrest in myeloid differentiation is caused by a genetic mutation that results in increasing numbers of circulating myeloid cells: neutrophils, basophils, and eosinophils, collectively known as granulocytes (which are themselves a type of leukocyte). The main function of granulocytes is to fight infection by bacteria and fungi. Granulocytes also regulate allergic reactions. In the chronic phase of the disease, these cells are functionally mature and the initial clinical features of the disease are a result of high levels of these granulocytes. Among patients who are symptomatic at presentation, symptoms of chronic myelogenous leukemia include fatigue, weight loss, fever, night sweats, bruising, aches in bones and joints, and swollen lymph nodes. Other patients are diagnosed following a routine blood test. Table 1 lists laboratory features characteristic of chronic myelogenous leukemia.

TABLE. Laboratory Features Characteristic of Chronic Myelogenous Leukemia

Diagnostic Modality	Features Characteristic of chronic myelogenous leukemia
Blood count	• Presence of leukocytosis (white blood count usually >25,000 per mm3). • Elevated basophils and granulocytes (particularly myelocytes).  Promyelocytes and  myeloblasts present  in small numbers unless patient has presented during blast crisis. • Erythrocyte and platelet counts may also be increased. • Mild anemia is present in 50% of cases at presentation. • Platelet count is abnormally high in 30-50% of cases.
Blood smear	• Morphology of white and red cells is normal. • Platelet morphology is usually normal but giant platelets may be present.
Bone marrow biopsy	• Marrow is hypercellular; an increase in the number of myeloid white blood cells occurs, particularly early myeloid forms.
Cytogenetic/molecular analysis	• Presence   of   Philadelphia  chromosome/BCR-/4BL   fusion gene.

In addition to increasing the number of circulating granulocytes, chronic myelogenous leukemia affects the maturation of bone marrow stem cells and causes an increase in blasts in the bloodstream and marrow. Blasts cannot carry out the functions of the mature granulocytes, resulting in anemia and increased risk of infection.

Chronic myelogenous leukemia is primarily a disease of adulthood. The median age at diagnosis is 55-60 years; less than 10% of cases occur in people under the age of 20. The disease in children is similar in behavior to that in adults, but the outcome of treatment with progenitor stem-cell transplantation — the only potentially curative therapy for chronic myelogenous leukemia — is better in these younger individuals. Although the median survival is five to seven years (based on patients treated in the pre-imatinib era), the range is wide: some patients die within one year of diagnosis, while others live for more than 15 years. The ratio of chronic myelogenous leukemia cases by sex is 1.4 male cases to 1 female case, but the clinical course is similar in both sexes.

Staging

Cytogenetic Changes

Prognostic Factors

Etiology

Chronic myelogenous leukemia is an acquired rather than an inherited condition; familial cases are rare and little evidence exists linking hereditary factors to chronic myelogenous leukemia. The offspring of patients with chronic myelogenous leukemia do not have a higher incidence of chronic myelogenous leukemia than does the general population, and there is no correlation in monozygotic twins. In the great majority of patients, a causative factor cannot be identified. Nevertheless, it is well known that ionizing radiation is a predisposing factor, as shown by studies of survivors of the Nagasaki and Hiroshima atomic bombs and of patients who have received radiotherapy for conditions such as cervical cancer.

The clinical progression of chronic myelogenous leukemia can be divided into the following three phases:

•  Chronic (blasts represent 5% or less of cells in blood and bone marrow).

•  Accelerated (blasts represent 6-30% of cells in blood and bone marrow).

•  Blastic (blasts represent 30% or more of cells in blood and bone marrow).

The chronic phase is characterized by a slow accumulation of granulocytes. This accumulation can be easily controlled, but not cured, with medication (inducing hematologic remission, i.e., normalization of blood cell counts and spleen size). Most patients are diagnosed while still in this phase, which varies in duration depending on the maintenance therapy used. The chronic phase usually lasts three to five years before it evolves into accelerated or blastic-phase disease.

In two-thirds of patients, the disease transforms gradually into the accelerated phase, at which point the leukemia is more difficult to manage and symptoms become more severe (the remaining one-third of patients progress straight to the blastic phase). During the accelerated phase, symptoms are caused by an increase in the number of granulocytes and blasts in the bloodstream. The survival of patients diagnosed in this phase averages 1 — 1.5 years.

The accelerated phase is a poorly defined stage for which no universally accepted definition exists. TABLE. Comparison of Three Classifications for Accelerated-Phase Chronic Myelogenous Leukemia shows three published classifications of accelerated phase. The criteria proposed by researchers from the M.D. Anderson Cancer Center in Houston, Texas, have been used most frequently in the recent studies of imatinib (Novartis’s Gleevec/Glivec), the gold-standard therapy for chronic myelogenous leukemia. The criteria of the International Bone Marrow Transplant Registry (IBMTR) are most frequently used in the bone marrow transplantation literature. The most recent classification, proposed by the World Health Organization (WHO), is not often employed.

After 3-18 months, the accelerated phase progresses to an acute blastic transformation, or “blast crisis.” The WHO recently proposed a change in the definition of the blastic phase; the organization suggested using a blast level in the blood of 20% as the threshold for diagnosis of this stage of disease. However, most of the available literature uses the standard cutoff of a 30% blast level in the blood. Skin or tissue infiltration by blasts also characterizes the blastic phase. Cytogenetic evidence of another Ph-positive clone or clonal evolution is usually present. At the blastic phase, the disease resembles acute leukemia. In the majority of patients, chronic myelogenous leukemia then transforms into a condition resembling acute myelogenous leukemia; in about 25% of patients, the leukemia takes on the appearance of acute lymphocytic leukemia.

TABLE. Comparison of Three Classifications for Accelerated-Phase Chronic Myelogenous Leukemia

Characteristic	M.D. Anderson Cancer Center (MDACC)	International Bone Marrow Transplant Registry (IBMTR)	World Health Organization (WHO)
Blasts (peripheral blood white cells or bone marrow cells) (%)a	>15	>10	10-19
Blasts + promyelocytes (%)a	>30	>20	NA
Basophils (%)a	>20	>20 (+ eosinophils)	>20
Platelets (x 109/L)	<100	Increasing and unresponsive to therapy or persistent decrease	<100 unrelated to therapy or > 1,000 unresponsive to therapy
WBC(x 109/L)	NA	Difficult to control, or doubling in less than five days	Increasing and unresponsive to therapy
Cytogenetic evidence of clonal evolution	Present	Present	Present
Anemia	NA	Unresponsive to therapy	NA
Splenomegaly	NA	Increasing	Increasing and unresponsive to therapy
Other	NA	Chloromas, myelofibrosis	Megakaryocyte proliferation, fibrosis, granulocytic dysplasia
Frequency of classifications’ use	High	Used in some bone marrow transplantation literature and clinical trials	Rare

^aAs a percentage of cells in blood and bone marrow. NA = Not applicable. WBC = White blood cell.

Whether the blast cells seen in blastic-phase disease are of myeloid or lymphoid lineage is an important distinction because it predicts the likely response to treatment and prognosis; patients with lymphoid blastic-phase disease have a better prognosis. Blastic-phase disease is generally resistant to treatment and is fatal within three to six months.

Rituximab (Rituxan, MabThera) is under development by Biogen Idee and Genentech in collaboration with Roche, Chugai, and Zenyaku Kogyo. This antibody is in Phase III clinical trials in the United States and Europe.

Rituximab is a mouse/human chimeric MAb directed against the cluster of differentiation (CD) 20 molecule. CD20 is a calcium channel that interacts with the B-cell immunoglobulinreceptor complex and is expressed on both normal and malignant B cells, making it an ideal target for monoclonal antibodies therapy in B-cell disorders. After binding to CD20, rituximab is thought to deplete B cells in a number of ways, including antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and alteration of calcium flux and factors involved in apoptosis. This antibody has been launched for the treatment of relapsed or refractory low-grade or follicular, CD20-positive B-cell non-Hodgkin’ s lymphoma (B-NHL).

Rituximab is under investigation in many chronic lymphocytic leukemia clinical trials both as a single agent and in combination with chemotherapy as well as in first- and subsequent-line settings.

The role for rituximab as a single agent in chronic lymphocytic leukemia is controversial. Previous studies showed an overall response rate of only 11% and 25%, comparing poorly with the rate of 40-60% reported for follicular NHL. However, a recent Nordic multicenter study yielded improved results. Twenty-four chronic lymphocytic leukemia patients of median age 57 (47-72) with active disease (3 Binet A, 7 Binet B, 14 Binet C) who had previously been heavily treated with a variety of chemotherapy regimens were given the standard dose of 375 mg/m² rituximab once weekly for four doses. The primary objectives this study addressed were response rate, quality, and duration; secondary objectives were to analyze the feasibility and tolerability of rituximab therapy.

Eight of 23 evaluable patients (35%) achieved a partial response (PR), with a median duration of 12.5 weeks. A drop of at least 50% in blood lymphocyte count occurred in 17/21 (81%) patients who had pretreatment lymphocytosis, and 10 patients achieved a normal blood lymphocyte count (< 3 x 10⁹ L^_1). Of the 15 patients who did not achieve a PR with rituximab, 9 had at least a 50% drop in lymphocyte count and 3 achieved a normal count.

TABLE. Emerging Therapies in Development for Chronic Lymphocytic Leukemia

Compound	Development Phase	Marketing Company
Monoclonal antibodies
Rituximab (Rituxan, MabThera)
United States	III	Biogen Idec/Genentech
Europe	III	Roche/Chugai/Zenyaku Kogyo
Japan	—	—
Lumiliximab (IDEC-152)
United States	II	Biogen Idee
Europe	—	—
Japan	—	—
Antisense oligonucleotides
Oblimersen (Genasense)
United States	Ill	Genta/Aventis
Europe	—	—
Japan	—	—
Cell-cycle inhibitors
Alvocidib (Flavopiridol)
United States	II	National Cancer Institute
Europe	III	—
Japan	—	—
Immunostimulatory therapies
Xcellerate
United States	I/I I	Invitrogen (formerly with Xcyte Technology)
Europe	—	—
Japan	—	—
ISF-154
United States	II	Tragen/University of California at San Diego
Europe	—	—
Japan	—	—
Immunotoxins
Denileukin diftitox (Ontak)
United States	II	Ligand Pharmaceuticals
Europe	—	—
Japan	—	—
Apoptosis inducers
SDX-101
United States	Ib/lla	Salmedix
Europe	—	—
Japan	—	—
Motexafin gadolinium (Xcytrin)
United States	II	Pharmacyclics
Europe	—	—
Japan	—	—
Selective apoptotic antineoplastic drugs
OSI-461
United States	Ila	OSI Pharmaceuticals
Europe	—	—
Japan	—	—

Seventy-five percent of patients experienced rituximab-related side effects, half of which were related to the first infusion only. The most common toxicities were World Health Organization (WHO) grade 1/2 chills and grade 2 fever. In previous studies, the severe infusion-related toxicities reported had been specifically linked to a high tumor burden. Mainly mild/moderate side effects were observed in this study, even in patients with extremely high lymphocytosis (223 x 10⁹ L^_1). This study demonstrates that single-agent rituximab does have some activity in heavily pretreated chronic lymphocytic leukemia patients, although the response is minor and of short duration.

The reasons rituximab is more effective in NHL than in chronic lymphocytic leukemia are unclear. Circulating soluble CD20 and a high tumor burden, both of which “mop up” rituximab, are potential mechanisms/states by which the antibody is rapidly cleared from the blood; this theory is supported by the observation of altered pharmacokinetics and increased response rates with higher doses of rituximab in chronic lymphocytic leukemia. In addition, chronic lymphocytic leukemia cells have a much lower density of surface CD20 than do NHL cells, although no correlation between density and response to therapy has been found.

Rituximab has been used as a first-line, single-agent therapy, and limited clinical data suggest it may be more effective than as second- or third-line therapy. In one trial, treatment-naive patients with stage II — IV small lymphocytic lymphoma or chronic lymphocytic leukemia received 375 mg/m² rituximab weekly for four doses. Patients who achieved an objective response (PR or complete response [CR]) or stable disease at reevaluation after six weeks continued maintenance courses of rituximab using the standard four-week schedule every six months for a maximum of four courses. Twenty-two of forty-three patients (51%) had an objective response at week 6, and the remaining patients had stable disease.

Twenty-eight patients (65%) went on to receive maintenance rituximab therapy. With a median follow-up of 24 months, the response rate was 58% (9% CR). Median progression-free survival (PFS) was 19 months with a one- and two-year actuarial PFS of 63% and 49%, respectively. Two patients had a reversible grade 3 infusion-related toxicity with the first course of rituximab. The increase in overall response rate is encouraging, but the small CR indicates that single-agent rituximab will not result in long-term survival in chronic lymphocytic leukemia.

Treatment for chronic lymphocytic leukemia is generally reserved for patients with symptoms of advanced disease, although rituximab therapy may be effective in early-stage disease for those at risk of progression. The overall response rate in 21 evaluable patients with Rai stage 0-11 and beta-2 microglobulin levels >2 mg/dL was 90% (19% CR, 19% nodular PR [nPR], 48% PR). The clinical significance of these results is unclear because a longer follow-up is required to analyze time to progression and long-term survival.

The dose and schedule of administration for single-agent rituximab therapy as both first and subsequent lines of therapy are under investigation in dose-escalation studies in an attempt to increase response rates. Researchers have reported using doses of up to 2,000 mg/m²/week in four patients. Such studies are ongoing to optimize clinical responses.

The most active area of research involving rituximab is in combination with chemotherapy. A randomized Phase II study of fludarabine in combination with concurrent rituximab versus sequential rituximab was conducted in 104 previously untreated chronic lymphocytic leukemia patients. The treatment schedule for sequential therapy involved patients receiving 25 mg/m² fludarabine for 5 days, repeated every 28 days for six cycles. Four weekly doses of 375 mg/m² rituximab were administered to patients who achieved stable disease or better, following a two-month rest period and restaging. The concurrent schedule followed the same pattern as the sequential schedule, with the addition of rituximab to each fludarabine cycle. It is important to note that patients receiving concurrent administration received 11 doses of rituximab (seven in combination with fludarabine and four as consolidation after this therapy) compared with only 4 doses in the sequential arm.

Concurrent administration of these two agents demonstrated superior response rates when compared with the sequential arm (47% CR versus 28% CR, 43% PR versus 49% PR, respectively). Neutropenia was more common in the concurrent arm, but infectious complications occurred at similar frequencies in both schedules. Additional data presented at the American Society of Hematology (ASH) meeting in 2003 determined that adding rituximab to fludarabine did not significantly increase the risk of infection.

This encouraging study establishes that concurrent administration of rituximab and fludarabine produces CR rates superior to those achieved with fludarabine alone. To date, the impact of rituximab on improving progression-free survival and overall survival compared with fludarabine monotherapy has not been analyzed in a randomized trial. A retrospective comparison with data from 179 patients enrolled in the North American Intergroup Study CALGB 9011 who received fludarabine monotherapy showed that CR, PR, and two-year performance-free and overall survival rates were significantly superior in the fludarabine/rituximab group.

The triple-drug regimen fludarabine/cyclophosphamide/rituximab (FCR) is also under intense investigation. In one study, 202 previously untreated chronic lymphocytic leukemia patients received FCR (25 mg/m²/day F for three days; 250 mg/m²/day C for three days; 375-500 mg/m² R on day 1). Results showed 68% CR, 18% nPR, and 14% PR. The study also analyzed patients for the presence of minimal residual disease (minimal residual disease) and found that the FCR regimen produced a high level of minimal residual disease-negative complete remissions. A longer follow-up will determine whether minimal residual disease-negative CR is more durable than minimal residual disease-positive CR.

At the 2003 ASH meeting, the results of a sequential FCR program also were presented. Thirty treatment-naive chronic lymphocytic leukemia patients received six cycles of standard fludarabine therapy, then 3 g/m² cyclophosphamide every three weeks for three cycles, and finally standard rituximab therapy. CR and PR rates of 57% and 29% (10% nPR and 19% PR), respectively, were achieved.

The FCR regimen has also succeeded in patients with relapsed or refractory chronic lymphocytic leukemia. In one trial, 179 patients who had already received between one and three courses of therapy were treated with FCR and achieved responses of 25% CR, 16% nPR, and 32% PR. Minimal residual disease (analyzed by polymerase chain reaction) was absent in 33% of CR patients. Therapy was well tolerated, and 62% of patients completed four or more cycles of this regimen. Forty-one percent of patients experienced fever and chills with the first rituximab infusion, and a minority experienced hypotension, nausea, and dyspnea (6%, 9%, and 3%, respectively). Hematologic toxicities included neutropenia in 30% of cycles and thrombocytopenia in 12%.

A comparative, retrospective analysis of patients treated with fludarabine (plus or minus prednisone), fludarabine/cyclophosphamide, or FCR demonstrated increased CR, overall response, and median survival in patients treated with FCR.

The purine analogue pentostatin (SuperGen Warner-Lambert’s Nipent) has shown significant activity and minimal toxicity when combined with cyclophos-phamide in chronic lymphocytic leukemia patients. In one trial, rituximab was added to this combination (known as the PCR regimen) and administered to previously untreated chronic lymphocytic leukemia patients. Preliminary data on 15 patients presented at ASH 2003 revealed 40% CR, 13% complete clinical response, and 47% PR. Most toxicities were grade 1 or 2, although eight patients suffered grade 3 anemia and hypotension and one patient developed grade 4 sinus bradycardia.

In another trial, 20 patients with relapsed or refractory disease were treated with the PCR regimen; the response rates were 20% CR, 10% nPR, and 50% PR. Grade 3/4 neutropenia occurred in 45% of patients, grade 3/4 thrombocytopenia in 5%, and infections in 15%. Preliminary data suggest this regimen is well tolerated, but further analysis is needed to determine both response rates and toxicity profiles compared with those associated with fludarabine-containing regimens.

The combination of rituximab and another MAb, alemtuzumab is under investigation for relapsed and refractory chronic lymphocytic leukemia. Nine patients underwent treatment with this combination, and preliminary data showed a 44% CR and 23% PR rate. Nonhematologic toxicities were grade 2 or less, and infection occurred in 44% of patients. Another study presented at ASH 2003 failed to show any complete or partial remissions in 11 patients with relapsed or refractory chronic lymphocytic leukemia who were treated with alemtuzumab and rituximab in combination. Further investigation into the combination of these antibodies is needed to determine their potential efficacy.

In an attempt to improve upon the success seen in FCR, the M.D. Anderson Cancer Center is pioneering a trial examining a regimen consisting of cyclophosphamide, fludarabine, alemtuzumab, and rituximab (known as the CFAR regimen). Only two relapsed/refractory patients have completed all courses, and both achieved PRs. Four patients on continuing therapy were evaluated after three courses, and responses included one CR, one nPR, and two PRs. Seven patients came off therapy because of treatment failure (n = 2), infection (n = 1), noncompliance (n = 1), or at their own request (n = 2); one death occurred as a result of disease-related liver failure. Early analysis indicates good response with substantial but expected toxicities.

Rituximab enjoys extensive off-label usage in the United States, mainly in the first- and second-line chronic lymphocytic leukemia settings in combination with chemotherapy. In Europe, however, the use of rituximab is restricted by a lack of reimbursement owing to its experimental status and high cost.

Nonpharmacological Approaches

Currently, the only potentially curative option for chronic lymphocytic leukemia is stem-cell transplantation, which is still a highly experimental approach. There are two main types of stem-cell transplantation: autologous, in which the patient’s own stem cells are harvested and then returned to his or her body, and allogeneic, in which a related or unrelated donor is the source of stem cells.

Allogeneic stem-cell transplantation carries the risk of the patient developing graft-versus-host disease, a condition in which the donated stem cells trigger an immune response against the patient. This complication can be fatal; indeed, allogeneic stem-cell transplantation carries a high risk of mortality. However, allogeneic stem-cell transplantation also provides a higher chance of cure, partly because of the graft-versus-leukemia effect, where by the donor’s stem cells trigger an immune response against the patient’s own leukemia cells. There is no risk of graft-versus-host disease in autologous stem-cell transplantation, but neither does the beneficial graft-versus-leukemia occur. Another disadvantage of autologous stem-cell transplantation is that harvested and donated stem cells may be contaminated with tumor cells, which are then returned to the patient. The relapse rate for patients treated with autologous stem-cell transplantation is high.

Current research is investigating allogeneic stem-cell transplantation in a nonmyeloablative, rather than fully ablative, setting. Nonmyeloablative stem-cell transplantation uses less intensive conditioning regimens that rely on immunosuppression rather than cytotoxicity. In general, stem-cell transplantation is used in a minority of patients who are young and have poor prognostic factors or as a last-chance option for patients with advanced disease.

Emerging Therapies

The emerging therapy market for B-cell chronic lymphocytic leukemia (chronic lymphocytic leukemia) is extremely sparse. Only two agents are in Phase III development, and of the agents in Phase II development, data are available on only a minority. Further, progress on agents such as Novartis’s protein kinase inhibitor midostaurin (PKC412) and Bioenvision/Ilex’s antimetabolite clofarabine (Clofarex) has not been published. Two immunotherapeutic approaches are in Phase II development for chronic lymphocytic leukemia: the University of Southampton in the United Kingdom is developing a DNA vaccine that produces anti-idiotype antibodies conjugated to tetanus toxin, and Immuno-Designed Molecules is developing IDM-4, a macrophage-activated killer-cell bispecific antibody. No clinical data are available on either of these agents. The proteasome inhibitor bortezomib (Millennium’s Velcade) has been extremely successful in the treatment of multiple myeloma and is under investigation for non-Hodgkin’s lymphoma. However, clinical trial data demonstrating its effect in chronic lymphocytic leukemia have not been published. For now, the focus remains fixed on monoclonal antibodies (monoclonal antibodies) to improve both response and overall survival rates in chronic lymphocytic leukemia.

TABLE. Emerging Therapies in Development for Chronic Lymphocytic Leukemia summarizes drug therapies in development for chronic lymphocytic leukemia.

Despite relatively good long-term survival rates, chronic lymphocytic leukemia  is considered incurable. For many years, first-line therapy was dominated by the oral alkylating agent chlorambucil (GlaxoSmithKline’s Leukeran). The introduction of purine analogues as monotherapy or in combination with alkylating agents into current treatment strategies has vastly improved response rates, although no improvement in overall survival has yet been noted.

Patients with chronic lymphocytic leukemia do not have a wide choice of therapy options. The overall population is elderly and has a low tolerance for toxic chemotherapy regimens. Once patients have failed both chlorambucil and fludarabine (Schering AG and Berlex’s Fludara), the disease becomes extremely difficult to treat. The aim of current drug regimens is to obtain the highest possible rate and duration of remission while balancing the associated toxicity and infection rate in these patients. TABLE. Current Regimens Used for Chronic Lymphocytic Leukemia describes the current regimens used to treat chronic lymphocytic leukemia.

TABLE. Current Regimens Used for Chronic Lymphocytic Leukemia

	Regimen Components		Dose
Regimen	Agent	Availability		Common Toxicities
Chlorambucil (single agent)	Chlorambucil (GlaxoSmith-Kline’s Leukeran)	US ,France,  Germany,  Italy, S, UK	Chlorambucil: 10 mg/m2/d on days 1 -7. Cycle repeated every 28 days.	•  Myelosuppression •  Mild gastrointestinal disturbances •  Increased risk of secondary malignancy
Fludarabine (single agent)	Fludarabine (Berlex’s Fludara, Schering’s Fludara/Fludar/ Bebeflur, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Fludarabine (oral): 40 mg/m2/d on days 1-5, (IV) 25 mg/m2/d on days 1 -5. Cycle repeated every 28 days.	•  Myelosuppression •  Increased infection •  Neurotoxicity •  Malaise/fatigue •  Nausea/vomiting •  Anorexia
Fludarabine/ cyclophosphamide (FC)	Fludarabine (Berlex’s Fludara, Schering’s Fludara/Fludar/ Bebeflur, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Fludarabine (oral): 40 mg/m2/d on days 1-3, (IV) 25 mg/m2/d on days 1 -3. Cycle repeated every 28 days.	•  Myelosuppression •  Increased infection •  Neurotoxicity (fludarabine) •  Alopecia (more common with cyclophosphamide)
	Cyclophosphamide (Bristol-Myers Squibb’s Cytoxan/ Endoxan/ Endoxana, Baxter’s Endoxan/ Endoxana, Shionogi’s Endoxan, Pfizer’s Neosar/Cyclostin, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Cyclophosphamide: 250 mg/m2/d on days 1 -3. Cycle repeated every 28 days.	•  Malaise/fatigue •  Nausea/vomiting •  Anorexia •  Hemorrhagic cystitis (cyclophosphamide) •  Neutropenia
Fludarabine/ cyclophosphamide/ mitoxantrone (FCM)	Fludarabine (Berlex’s Fludara, Schering’s Fludara/Fludar/ Bebeflur, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Fludarabine (oral): 40 mg/m2/d on days 1-3, (IV) 25 mg/m2/d on days 1 -3. Cycle repeated every 28 days.	•  Myelosuppression •  Increased infection •  Neurotoxicity (fludarabine) •  Alopecia (more common with cyclophosphamide)
	Cyclophosphamide (Bristol-Myers Squibb’s Cytoxan/ Endoxan/ Endoxana, Baxter’s Endoxan/ Endoxana, Shionogi’s Endoxan, Pfizer’s Cyclostin, generics) Mitoxantrone (Serono Lab/Wyeth/ Takeda’s Novantrone, Baxter’s Onkotrone, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan US ,France,  Germany,  Italy, Spain,  UK, Japan	Cyclophosphamide: 200 mg/m2/d on days 1 -3. Cycle repeated every 28 days. Mitoxantrone: 6 mg/m2/d on day 1. Cycle repeated every 28 days.	•  Malaise/fatigue •  Nausea/vomiting •  Anorexia •  Hemorrhagic cystitis (cyclophosphamide •  Cardiac toxicity (mitoxantrone)
CHOP	Cyclophosphamide (Bristol-Myers Squibb’s Cytoxan/ Endoxan/ Endoxana, Baxter’s Endoxan/ Endoxana, Shionogi’s Endoxan, Pfizer’s Neosar/Cyclostin, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Cyclophosphamide: 750 mg/m2/d on day 1. Cycle repeated every 28 days.	•  Myelosuppression •  Increased infection •  Alopecia •  Malaise/fatigue •  Nausea/vomiting •  Anorexia •  Hemorrhagic cystitis (cyclophosphamide)
	Doxorubicin (Pfizer’s Adriamycin/ Adriblastine, Bristol-Myers Squibb’s Rubex, Kyowa’s Adriacin, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Doxorubicin: 50 mg/m2/d on day 1. Cycle repeated every 28 days.
	Vincristine (Eli Lilly/EG Labo/Lilly-Shionogi’s Oncovin, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Vincristine: 1.4 mg/m2/d on day 1. Cycle repeated every 28 days.
	Prednisone3 (generics)	US ,France,  Germany,  Italy, Spain	Prednisone/ Prednisolone: 50 mg/m2 on days 1-5. Cycle repeated every 28 days.
	Prednisolone (generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan
Cyclophosphamide, Vincristine, Prednisone	Cyclophosphamide (Bristol-Myers Squibb’s Cytoxan/ Endoxan/ Endoxana, Baxter’s Endoxan/ Endoxana, Shionogi’s Endoxan, Pfizer’s Neosar/Cyclostin. generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Cyclophosphamide: 750 mg/m2/d on day. Cycle repeated every 28 days.	•  Myelosuppression •  Increased infection •  Alopecia •  Malaise/fatigue •  Nausea/vomiting •  Anorexia •  Hemorrhagic cystitis (cyclophosphamide)
	Vincristine (Eli Lilly/EG Labo/Lilly-Shionogi’s Oncovin, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Vincristine: 1 mg/m2/d on day 1. Cycle repeated every 28 days.
	Prednisone3 (generics)	US ,France,  Germany,  Italy,   S	Prednisone/ Prednisolone: 50 mg/m2 on days 1-5. Cycle repeated every 28 days.
	Prednisolone (generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan
Pentostatin/ cyclophosphamide	Pentostatin (SuperGen/ Wyeth/ Pfizer’s Nipent, Nihonkayaku’s Coforin)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Pentostatin: 4 mg/m2/d on day 1. Cycle repeated every 28 days.	•  Myelosuppression (mild) •  Increased infection •  Malaise/fatigue •  Fever •  Nausea/vomiting •  Anorexia •  Hemorrhagic cystitis (cyclophosphamide)
	Cyclophosphamide (Bristol-Myers Squibb’s Cytoxan/ Endoxan/ Endoxana, Baxter’s Endoxan/ Endoxana, Shionogi’s Endoxan, Pfizer’s Cyclostin, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Cyclophosphamide: 600 mg/m2/d on day 1. Cycle repeated every 28 days.
Cladribine (single agent)	Cladribine (Ortho-Biotech’s Leustatin, Japananssen-Cilag’s Leustatin/ Leustatine/ Leustat, generics)	US ,France,  Germany,  Italy, Spain,  UK, Japan	Cladribine: 0.14 mg/kg/d on days 1 -5.	•  Myelosuppression •  Increased infection •  Malaise/fatigue •  Fever •  Rash •  Headache
Alemtuzumab (single agent)	Alemtuzumab (Berlex’s Campath, Schering’s Mab Campath)	US ,France,  Germany,  Italy, Spain,  UK	Alemtuzumab: escalating dose of 3, 10,30 mg/d for week 1, followed by 30 mg/d for 3 days per week.	•  Myelosuppression •  Increased infection •  Anemia •  Fever •  Nausea/vomiting •  Rash •  Fatigue •  Urticaria •  Rigors • Transient Cytopenia

a. Prednisolone is used where prednisone is not available.

IV = Intravenous; MAB = Monoclonal antibody.

Chlorambucil (Single Agent)

Overview

For the past 40 years, first-line treatment of chronic lymphocytic leukemia has been limited mainly to the alkylating agent chlorambucil (GlaxoSmithKline’s Leukeran). Although newer agents are being used with increasing frequency, chlorambucil still garners a significant patient share in the United States, France, Germany, Italy, Spain, and the United Kingdom. This popularity is the result of its preferable toxicity profile, which is advantageous in chronic lymphocytic leukemia — a disease with an elderly population that is less able to cope with high toxicities.

Mechanism Of Action

Chlorambucil is an alkylating agent. Alkylation of DNA results in breaks in the DNA molecule as well as cross-linking of the twin strands, thus interfering with DNA replication and transcription of RNA and ultimately causing cell death.

Clinical Performance

A variety of schedules are in use. Chlorambucil is an agent that can be administered with or without the corticosteroids prednisone or prednisolone (both generic). No evidence from randomized trials exists to prove that adding a corticosteroid enhances the efficacy of chlorambucil or other alkylating agents. However, physicians often include them in cases of bulky disease requiring a rapid response or when chlorambucil produces severe hematologic toxicity.

First-line chlorambucil therapy (plus or minus prednisone) in untreated chronic lymphocytic leukemia patients produces complete response rates of 4-12% and overall response rates of approximately 40-60%. Recent trials have shown that first-line fludarabine therapy (discussed later) provides superior response rates compared with chlorambucil; however, the two compounds’ long-term survival rates are not significantly different.

Chlorambucil does have a less toxic side-effect profile and is therefore the preferred therapy in older patients (65 or older) and those with a poor performance status who are unable to tolerate the severe myelosuppression caused by fludarabine. Another well-established benefit of chlorambucil is its oral formulation, although an oral formulation of fludarabine has become available in some countries.

No etiologic factors have been clearly defined for chronic lymphocytic leukemia, although few studies have been performed. Most chronic lymphocytic leukemia cases occur sporadically, but approximately 1 in 20 patients has a familial form of the disease. The presence of familial cases clearly suggests that inherited genetic factors contribute to the development of the disease, although the specific abnormal genes connected to chronic lymphocytic leukemia have not yet been identified. The incidence of chronic lymphocytic leukemia in first-degree relatives is three times greater than in the general population (3 in 10,000, compared with 1 in 10,000).

TABLE.Common Cytogenetic Changes in Chronic Lymphocytic Leukemia and Their Significance

Marker (Mutation)	Frequency of Marker (96)	Significance of Mutation and Additional Comments
Deletions in chromosome 13	35-55	Associated with benign disease (stable or slowly progressing); patients with this marker survive as long as age-matched controls.
Additional chromosome 12	15-20	Associated with atypical morphology, aggressive disease, and poor prognosis; patients tend to have unmutated immunoglobulinvariable genes.
Deletions in chromosome 11	15-20	Patients have more aggressive disease; patients who are carriers of the ATM genes found on chromosome 11 may be at greater risk of developing chronic lymphocytic leukemia.
Defects in chromosome 17 affecting the p53 oncogene	15	Associated with advanced disease, high proliferation rate, shortened survival, resistance to chemotherapy, and increased likelihood of Richter’s syndrome.

ATM = Ataxia-telangiectasia mutated.

Chronic lymphocytic leukemia is less common in the Japanese and other Asian populations than in populations originating in the Western world, and the incidence does not increase in Asian expatriates.

Environmental factors such as ionizing radiation, chemicals, and viruses do not seem to be associated with the pathogenesis of this disease.

Mature blood cells (red cells, white cells, and platelets) are produced in the bone marrow from pluripotent hematopoietic stem cells. (FIGURE.The hematopoietic cascade: development of mature blood cells from pluripotent hematopoietic stem cells shows the different lineages of blood cells and the stages involved in their maturation.) The blood cells mature and differentiate through a sequence of steps involving a series of complex — and incompletely understood — interactions with growth factors, cytokines, and other cells in the bone marrow. Once mature, the blood cells leave the bone marrow and enter the general circulation, where they have a limited life span.

T and B lymphocytes (often known as T and B cells) are white blood cells, and they are vital constituents of the immune system. When the body is infected with a pathogen, T and B cells are mobilized to target and kill the pathogen. Although other immune cells are involved in this process, lymphocytes possess unique qualities that allow them to adapt during infection and become specific to the invading pathogen. In addition, once an infection has been cleared from the body, most of these lymphocytes die, but a few “memory” lymphocytes remain. Upon future reinfection with the same pathogen, these cells are immediately activated, so each successive immune response is therefore quicker and more accurate than the one before.

FIGURE.The hematopoietic cascade: development of mature blood cells from pluripotent hematopoietic stem cells.

Cancer occurs when a series of genetic mutations, which are hereditary and/or environmental in nature, takes place in a single cell. The resulting cell proliferates without control and disrupts the normal functioning of the organ in which it originates. A lymphoid leukemia results when this process occurs in a T or B lymphocyte, and the expanding malignant cells disrupt the balance of normal blood cells in the bone marrow, blood, and lymphoid organs.

Lymphoid leukemias can be acute or chronic and can arise from lymphocytes at different stages of developmentChronic lymphocytic leukemia is a malignancy of small, morphologically mature but immunologically less mature lymphocytes that accumulate in the blood, bone marrow, lymph nodes, spleen, and liver. No single defined genetic mutation or abnormality is solely responsible for all chronic lymphocytic leukemia cases; instead, this disease is characterized by an array of different chromosomal deletions (described later). Investigators have also described a multitude of aberrations associated with apoptotic proteins, suggesting that in most cases, chronic lymphocytic leukemia cells accumulate as a result of an abnormally long life span rather than an accelerated rate of proliferation.

The median age of onset of chronic lymphocytic leukemia is 65-68 years, although approximately 20% of cases occur in people younger than age 55. Survival is dependent on the stage of disease and ranges from a median of 12 years in patients with the earliest stage to 2-5 years in those with advanced disease. Chronic lymphocytic leukemia also tends to occur more in men than in women. Onset is usually insidious, and up to 70% of patients are asymptomatic. Diagnosis is often made following routine blood tests or investigations for an unrelated disease. In symptomatic patients, the most frequent clinical findings are fatigue, loss of appetite, weight loss, and enlarged lymph nodes. Table 1 lists laboratory features typical of chronic lymphocytic leukemia.

Chronic lymphocytic leukemia has no single pattern of progression — approximately one-third of patients never require treatment and die from causes unrelated to chronic lymphocytic leukemia; one-third have an initial indolent phase followed by progression; and the remaining third have aggressive disease at the outset requiring immediate therapy.

Chronic lymphocytic leukemia’s progressive symptoms are related to leukocyte infiltration of the bone marrow, spleen, and lymphoid tissue. This infiltration, together with disruptions in normal hematopoietic function, results in anemia, neutropenia, thrombocytopenia, and immunological dysfunction. The most important immunological dysfunction is the lack of immunoglobulins (hypogammaglobulinemia), a condition that occurs in up to 60% of patients with advanced disease. This condition leaves the patient more susceptible to infection, which is a primary cause of death and morbidity.

Autoimmune disease, an immune response against the body’s own cells and tissues, occurs in 10-35% of untreated chronic lymphocytic leukemia patients. This condition is a natural complication of chronic lymphocytic leukemia but is also associated with purine analogue therapy (a common treatment for chronic lymphocytic leukemia); however, the exact frequency of treatment-induced autoimmune disease is unknown. The autoimmunity usually manifests as autoimmune hemolytic anemia. Immune thrombocytopenia, pure red-cell aplasia, and immune neutropenia occur less frequently. Autoimmunity is usually successfully treated with corticosteroids; steroid-refractory patients may have to undergo a splenectomy.

In 3-10% of patients with chronic lymphocytic leukemia, the disease undergoes a transformation into a more aggressive condition distinct from chronic lymphocytic leukemia. The transformation is usually into large-cell lymphoma (also known as Richter’s syndrome), and the prognosis for these patients is poor — median survival is six months. Transformation into prolymphocytic leukemia occurs occasionally, and transformation into acute leukemia is rare.

TABLE. Laboratory Features Characteristic of Chronic Lymphocytic Leukemia

Diagnostic Modality	Features Characteristic of Chronic Lymphocytic Leukemia
Blood count	• >5,000 lymphocytes/microliter of peripheral blood. • Anemia and thrombocytopenia present at the time of initial diagnosis in approximately 20% of patients; both are usually mild, but their presence denotes a poor prognosis. • Polyclonal increases in gamma globulins (present in approximately 15% of patients). • Hypogammaglobulinemia (8%). • Autoimmune thrombocytopenia (3%). • Pure red-cell aplasia (0.5%). • Agranulocytosis (0.5%).
Blood smear	• A large number of small, morphologically mature-appearing lymphocytes are visible; the nucleus is large, a nucleolus usually not evident, and only a thin band of cytoplasm is evident (a small proportion of lymphocytes may be larger with a larger nucleus and a visible nucleolus).
	• “Smudge cells” (ruptured cells) may be visible; these are lymphocytes that appear flattened or smudged in the process of slide preparation.
	• When leukocyte counts are extremely high (in excess of 200,000/mL), whole blood viscosity may be abnormally high.
Bone marrow biopsy	• The proportion of mature-appearing lymphocytes in the bone marrow aspirate exceeds 30% of all nucleated cells.
	• Infiltrative patterns of lymphocytes that may be nodular (10%), interstitial (30%), or diffuse (35%). A mixture of infiltrative patterns is observed in 25% of patients.
	• The infiltration pattern is significant in determining prognosis; diffuse infiltration is associated with advanced disease and poorer prognosis, whereas nodular and interstitial patterns (nondiffuse) are associated with less-advanced disease and better prognosis.
Cytogenetic/molecular analysis	• Cytogenetic analysis is undertaken in research settings only.
Immunophenotypical analysis	• Low levels of surface immunoglobulin, only a single light chain.
	• Expression of one or more B-cell-associated antigens -CD19, CD20, andCD23.
	• Coexpression of CD5.

Classification

The World Health Organization (WHO) published a consensus classification system that categorizes lymphoid disorders based on morphology, immunophenotype, genetic features, and clinical characteristics. Under the WHO classification system, chronic lymphocytic leukemia and small lymphocytic lymphoma (the lymphoid form of chronic lymphocytic leukemia) are grouped into a single entity (chronic lymphocytic leukemia).

Advances in monoclonal antibody and flow cytometry technology have established immunophenotyping as a routine diagnostic test for chronic lymphocytic leukemia. Using these methods, chronic lymphocytic leukemia is easily distinguished from other B-cell neoplasms because the cells aberrantly express CD5, a T-cell marker.

Staging

Prognostic Factors

Three major staging systems exist for the classification of chronic lymphocytic leukemia. (These systems are described in TABLE.Common Staging Systems Used in the Treatment of Chronic Lymphocytic Leukemia).

The original Rai system, published in 1975, consists of stages 0-IV and is based on the presence of lymphadenopa-thy, organomegaly, and cytopenias, demonstrating a correlation between Rai stage and survival. This system was later modified from the five-tier system to a three-tier system that categorizes patients as having a low, intermediate, or high risk of disease progression.

TABLE.Common Staging Systems Used in the Treatment of Chronic Lymphocytic Leukemia

System	Stage	Definition
Rai staging system	0	Lymphocytosis only
	I	Lymphocytosis and lymphadenopathy
	II	Lymphocytosis, spleen or liver enlargement
	III	Lymphocytosis and anemia (hemoglobin <11 g/dL)
	IV	Lymphocytosis and thrombocytopenia (platelet count < 100,000 mL)
Modified Rai staging system	Low risk of progression	Rai stage 0
	Intermediate risk of progression	Rai stage I or II
	High risk of progression	Rai stage III or IV
Binet staging system	A	Lymphocytosis, with enlargement of <3 lymphoid areas3; no anemia or thrombocytopenia
	B	Lymphocytosis, with enlargement <3 lymphoid areas
	C	Lymphocytosis and either anemia (hemoglobin <10 g/dL) or thrombocytopenia (platelet count <100,000/mL), or both

a. The following lymphoid areas are included: cervical, axillary, inguinal (whether unilateral or bilateral), spleen, and liver.

The Binet classification system (A, B, C) was devised based on a retrospective analysis of disease burden that draws a correlation between the number of nodal groups involved with disease and bone marrow failure. The National Cancer Institute (NCI)’s guidelines for chronic lymphocytic leukemia state that the major distinctions and benefits of the Binet system derive from its recognition that (1) a predominantly splenic form of the disease may have a better prognosis in the Binet system than in the Rai systems, (2) patients with comorbid anemia or thrombocytopenia have a similar prognosis, and (3) the presence of either of these two conditions can be grouped in the same stage rather than in separate stages.

Although both the Rai and Binet systems group patients according to their risk of progression, the early stages of disease do not correspond well between the two systems. Binet’s good prognosis group, A, includes twice as many patients as Rai’s stage 0 because it includes all Rai stage 0, two-thirds of Rai stage I, and one-third of Rai stage II. The original and modified Rai systems are used throughout the United States; all three systems are used in Europe, although physicians quote Binet more frequently. The overlap among staging systems has made the comparison of clinical trials using different staging systems difficult.

Although the Rai and Binet staging systems each give general indications as to a patient’s prognosis, survival within each stage can vary significantly, particularly in those patients with Binet stage A and Rai stage 0. As many as 30% of these patients have “smoldering” chronic lymphocytic leukemia, which progresses slowly and never requires therapy; other patients have more progressive disease that will eventually require treatment and may be fatal. The median survival of patients with Rai stage 0 exceeds 12 years and may reach 20 years with a 10-year overall survival rate of 70-75%. Patients with Rai stage I and II have a median survival of 8-10 years and 5-8 years, respectively, whereas recent data show a median survival of 5 years and longer in Rai stage III and IV patients.

Chronic lymphocytic leukemia is heterogeneous in both molecular pathology and clinical course, and many questions regarding the most appropriate management of this disease remain unanswered. Researchers continue to investigate both biological and clinical parameters in an attempt to refine the staging systems and accurately determine the prognostic outcome for patients with chronic lymphocytic leukemia and to individualize treatment. We discuss the most common markers further on, but many other markers, including interleukin (IL)-6, IL-10, tumor necrosis factor, intra-cellular BCL-2, vascular endothelial growth factor, and other cytokines and enzymes, are being investigated for their potential prognostic significance.

Lymphocyte Doubling Time

The lymphocyte doubling time is calculated as the number of months it takes the absolute lymphocyte count to double in number. This factor has been confirmed as a prognostic indicator that is independent of stage in a variety of studies. After a 118-month

follow-up, median survival was 61 months in patients with an lymphocyte doubling time of less than 12 months, and median survival was not yet reached in patients with an lymphocyte doubling time  of more than 12 months. According to published literature, this factor is subject to variation.

Serum Beta-2 Microglobulin

The serum marker beta-2 microglobulin correlates with tumor burden and disease stage in patients with chronic lymphocytic leukemia. A retrospective study from the M.D. Anderson Cancer Center (Houston, TX) found this serum marker to be the strongest predictor of five-year survival in a multivariate analysis that controlled for age, sex, and performance status. Similar results have been reported in other retrospective trials; however, a prospective trial did not find beta-2 microglobulin to be a significant predictor of survival in a multivariate analysis that controlled for stage and lymphocyte doubling time. Additional studies are required to further classify the role of beta-2 microglobulin in prognosis.

Immunoglobulin Mutation Status

The B-cell antigen receptor, or immunoglobulin, is a surface molecule that detects the presence of pathogenic antigens and activates an immune response. Its synthesis during B-cell development occurs via a process of gene rearrangement. Gene segments are selected and assembled in such a way that each B lymphocyte produces an immunoglobulinthat is unique to that cell. When the B lymphocyte encounters an antigen, the immunoglobulinmolecule is altered by a process known as somatic hypermutation, which makes the immunoglobulin more specific for the antigen, thus enhancing the immune response. The presence of mutations in an immunoglobulinis evidence of its encounter with antigen and a marker of B-cell maturity.

Chronic lymphocytic leukemia was initially thought to be a malignancy of antigen-naive B cells with unmutated immunoglobulin. Researchers subsequently found that a subset of chronic lymphocytic leukemia patients had mutated immunoglobulin, suggesting the cell of origin was more mature and had encountered antigen. In 1999, two studies simultaneously reported the prognostic significance of immunoglobulin mutation status in chronic lymphocytic leukemia. The studies demonstrated that patients with a mutated immunoglobulin status had significantly longer survival than those with unmutated immunoglobulin. Many studies have confirmed the prognostic significance of immunoglobulin mutation, and researchers have established correlations between immunoglobulin mutation status and the need for chemotherapy, the response to chemotherapy, and the risk of relapse after transplantation.

Serum Thymidine Kinase

Thymidine kinase is an enzyme involved in the DNA synthesis salvage pathway, a process required for the synthesis of new DNA precursors in dividing cells. Present in dividing cells and absent in resting cells, it is a marker of proliferation. A recent study demonstrated the relationship between serum thymidine kinase level and mutation status: a level greater than 15 U/L was a strong predictor of unmutated immunoglobulin genes. Other studies have described a relationship between thymidine kinase level and lymphocyte doubling time, lymphocyte count, and beta-2 microglobulin. This enzyme has also been shown to be a significant predictor of survival and response to treatment. Commercial assays are available for the measurement of this enzyme. Additional large-scale studies are required to determine its prognostic importance in multivariate analyses.

CD38. CD38 is a cell-surface molecule expressed by mature B cells. Its expression on chronic lymphocytic leukemia cells has been shown to have prognostic significance in univariate and multivariate analyses, which have included clinical-stage, cytogenetic abnormalities and beta-2 microglobulin levels. CD38 expression has been associated with unmutated immunoglobulin status, though results are discordant in approximately 30% of cases. Whether CD38 has prognostic significance in patients with known immunoglobulin mutation status is controversial. This marker may also vary during the course of disease. CD38 is reportedly a useful and easily measured prognostic marker, but it is limited by differences in expression over time for individual patients and is not a surrogate for immunoglobulin mutation status.

ZAP70. ZAP70 is a signaling molecule involved in transducing intracellular signals from the T-cell receptor to the nucleus in T lymphocytes. This molecule was found to be aberrantly expressed in malignant chronic lymphocytic leukemia B cells that have unmutated immunoglobulin genes. The aberrant expression of ZAP70 in this subset of chronic lymphocytic leukemia cells was discovered by microarray gene chip expression profiling and confirmed by protein analysis. It was also found to be elevated in chronic lymphocytic leukemia cells that are CD38-positive. A flow cytometric assay that could identify ZAP70 expression is under investigation. Although promising, additional studies are needed to further define the prognostic value of this marker in relation to other chronic lymphocytic leukemia markers.

Cytogenetic Abnormalities

As many as 80% of chronic lymphocytic leukemia patients have identifiable cytogenetic abnormalities, although these problems are more common in patients with advanced disease than in those with early-stage disease. No single specific abnormality or gene has been consistently correlated with the pathogenesis of chronic lymphocytic leukemia, and any relationship between the genetic changes and the evolution of the disease has yet to be fully elucidated.

The most common cytogenetic changes found in chronic lymphocytic leukemia are deletions in chromosomes 11, 13, and 17, and the presence of an additional chromosome 12. Deletions in chromosome 17 are associated with p53 oncogene inactivation. These chromosomal abnormalities have prognostic significance (TABLE. Common Cytogenetic Changes in Chronic Lymphocytic Leukemia and Their Significance) and affect treatment decisions in hospitals where the technology is available to perform the analysis.