Chronic lymphocytic leukemia (CLL) is a clonal disease characterized by proliferation and accumulation of small CD5 positive B-cells. It is the most common leukemia in the western world accounting for approximately 30% of all leukemias in Europe and North America with an incidence of 4:100.000/year (1). The disease is diagnosed most commonly in the elderly. The median age at diagnosis is 65-70 years with 80% of patients diagnosed over 60 years of age. The natural clinical course of CLL is highly variable and chemotherapy is usually not indicated in an early and stable disease. However, patients with progressive and more advanced disease require treatment (2).

Clinical staging systems proposed in the early 1980’s by Binet et al.(3) and Rai et al (4) are still the most common and validated prognostic factors in the patients with CLL. Within the past few years, several biological markers, including serum markers, immunoglobulin heavy chain variable region (IgV_H) mutation status, some cytogenetic abnormalities, P53 mutations, cell membrane expression of CD38 and intracellular expression of zeta-associated protein-70 (ZAP-70), have become important prognostic factors (5). A correlation between the immunoglobulin gene mutational status and prognosis has shown that the median survival for stage A patients with unmutated IgV_H genes was 8 years, compared with approximately 25 years for patients with mutated IgV_H genes.

Deletion of 11q22-q23 and deletion of 17p13 are independent prognostic factors identifying patients with a rapid disease progression and a short survival time in a multivariate analysis (6). The deletion 17p affecting the TP53 gene has been associated with failure after treatment with alkylating agents, purine analogs, and rituximab (7). In contrast, deletion of chromosome band 13q14 is associated with a favourable outcome. Moreover, patients with trisomy 12 have a shorter survival than those with 13q deletion. Deletion of 17p and deletion of 11q predominate among advanced stages of CLL and among patients with unmutated IgV_H genes. In patients with CLL deletion 17p13 is independent prognostic factor identifying patients with rapid disease progression and short survival time. Furthermore, ZAP-70 expression and CD38 expression on leukemic lymphocytes have been found to correlate with IgV_H mutations and a shorter patient survival . Recent data may indicate that a prognostic score constructed using modified Rai stage, cellular CD38 and serum lactate dehydrogenase (LDH) significantly predict time to treatment failure and survival in patients at the time of diagnosis, and perform as well or better than models using the newer markers. The expression of ZAP-70 remains constant over the course of the disease as opposed to CD38. ZAP-70 expression can be evaluated using flow cytometric techniques, immunohistochemistry, western blotting or reverse transcriptase-polymerase chain reaction techniques. The cut-off to classify patients as ZAP-70 positive or ZAP-70 negative remains controversial and arbitrarily varies between 10% and 20%. Standardization of its measurement at the messenger RNA (mRNA) or protein level needs further investigation. Several serologic parameters such as thymidin kinase (TK), β2-microglobulin (β2M) and soluble CD23 (sCD23) provide also valuable information about the disease progression and survival.

There is no evidence that cytotoxic therapy has beneficial effects in patients with the indolent form of the disease (9, 10). However, patients with symptomatic and/or progressive disease should be immediately treated.

Widely accepted guidelines for the initiation of chemotherapy in CLL patients have been proposed by the National Cancer Institute Sponsored Working Group (NCI-WG) (11, 12). According to these guidelines the criteria for the initiation of therapy may not be identical for routine clinical practice and for patients included in clinical trials. In the routine clinical practice, therapy should not be initiated in patients who have asymptomatic CLL, including those with Rai stage 0 or Binet stage A until disease progression or unless disease-related symptoms are evident. Laboratory results supporting deferred therapy include a non-diffuse pattern of bone marrow involvement, serum haemoglobin concentration > 13 g/dL, peripheral blood lymphocytes < 30 × 10⁹/L, and lymphocyte doubling time longer than 12 months. The criteria for treatment initiation include disease-related symptoms, especially fever, body weight loss and extreme fatigue, increasing bone marrow failure, autoimmune anaemia and/or thrombocytopenia responding poorly to corticosteroid treatment, massive or progressive splenomegaly and/or lymphadenopathy, progressive lymphocytosis and recurrent infections.

For many years, chlorambucil has been considered the drug of choice in previously untreated patients. Higher response rates were obtained when higher doses of chlorambucill were used (13). Chlorambucil is still acceptable as the first line treatment of progressive CLL in frail, elderly patients with comorbidities, because of the apparent increase in toxicity of purine nucleoside analogs (PNAs) in this group of patients. The recent results of the German CLL study group (GCLLSG) support such a recommendation (14).

Bendamustine (Treanda; Cephalon), is a bifunctional alkylating agent composed of an alkylating nitrogen mustard group and a purine like benzimidazole ring. This agent seems to have a low cross-resistance with alkylating agents and fludarabine. Bendamustine have been investigated in several clinical trials (15). Various doses and treatment schedules have shown significant efficacy and acceptable toxicity in previously treated patients. The dose of 70 mg/m² on days 1 and 2 every 4 weeks is suggested in heavily pretreated and treatment-refractory patients. Bendamustine was also investigated in an open-label, randomized, comparative trial (16). Previously untreated patients were randomly assigned to receive either bendamustine (100 mg/m² i.v. on days 1 and 2) or chlorambucil (0.8 mg/kg p.o. on days 1 and 15). An overall response rate and a CR rate were significantly higher in patients treated with bendamustine. Moreover, the median duration of response was longer after treatment with bendamustine (21.7 months) than after chlorambucil (9.3 month, p < 0.0001). Other alkylating agents have been less extensively investigated than chlorambucil and mainly in combination therapy. Cyclophosphamide (CY) has a similar activity to chlorambucil and is usually used when chlorambucil is poorly tolerated. Cyclophosphamide was more frequently used in combination therapy with vincristine and prednisone (COP, CVP) or with doxorubicin, vincristine and prednisone (CHOP) (10).

In the past 20 years the purine nucleoside analogs (PNA) – fludarabine (FA), cladribine (2-CdA, 2-chlorodeoxyadenosine) and pentostatin (DCF, 2’-deoxycoformycin) have been introduced for treatment of CLL (10,13). Significantly higher OR, CR, and longer progression free survival (PFS) in patients with CLL treated with FA or 2-CdA have been confirmed in randomized, multicenter trials and more recently in meta-analysis. However, the median survival time did not differ between patients treated with PNA and alkylating agents. Combination therapies with PNA and CY are more active than monotherapy in terms of OR, CR and PFS. However, higher overall response (OR), CR and PFS do not translate for longer overall survival. Over the last few years several monoclonal antibodies (mAbs) and immunotoxins have been investigated in clinical trials in patients with CLL Recently, we performed a randomized study that compared the activity and toxicity of 2-CdA and CY (CC programe) versus FA and CY (FC programe) in previously untreated progressive or symptomatic CLL (2). We did not observe any significant differences in CC and FC efficacy and toxicity across different patient prognostic subgroups (17).

Over the last few years several monoclonal antibodies (mAbs) and immunotoxins have been investigated in clinical trials in patients with CLL (18). The most important clinical value in the patients with CLL have at present two antibodies. The first is human mouse antibody rituximab that targets CD20 antigen. The second is alemtuzumab, a humanized form of a rat antibody active against CD52.

Rituximab (Rituxan, Mabthera, F. Hoffmann-La Roche) is an IgG1 kappa immunoglobulin containing murine light – and heavy-chain variable region sequences and human constant region sequences (18, 20). The Fab domain of the rituximab binds specifically to the CD20 antigen, expressed on normal and malignant B-lymphocytes. The Fc domain recruits immune effect or functions to mediate B-cell lysis in vitro and in vivo.

The precise mechanism of rituximab cytotoxicity remains unclear. However, several mechanism by which rituximab may be cytotoxic are suggested. These include complement-dependent cytotoxicity (CDC), which involves fixation of the complement by the Fc portion of immunoglobulin and the subsequent activation of the complement cascade. Moreover, rituximab induces antibody-dependent cell mediated cytotoxicity (ADCC) in vitro. These two mechanisms are categorized into “immune-mobilizing” mechanisms or direct effects. However, accumulating evidence suggests that rituximab can also directly induce apoptosis.

Rituximab in conventional doses of 375 mg/m² weekly for 4 doses has rather low efficiency in CLL. In the study performed by Byrd et al. 83 previously treated CLL patients were treated with different doses of rituximab (250 mg/m²-375 mg/m²) 3 times weekly for 4 weeks (20). The OR rate was 45% (3% CR and 42% PR). Responses were noted in all groups of patients including those with bulky lymphadenopathy and those for which alkylator and/or FA based therapy had failed. However, some studies suggest that higher doses are more effective than standard doses, used routinely in other lymphoid malignancies O’Brien et al. treated CLL patients with an initial dose of rituximab 375 mg/m² which was then increased to a fixed dose of between 500 and 2250 mg/m² once weekly for 4 weeks (21). The OR rate was 36% and ranged between 22-75%. All responses were partial responses (PR). Median time to progression in responded patients was 8 months with the longest remission duration 15 + months.

Several recent reports suggest that in patients with CLL, rituximab combined with PNA can increase the OR and CR rates and prolonge PFS as compared with PNA or rituximab alone with acceptable toxicity. The addition of rituximab to a variety of chemotherapy regimens for the treatment of patients with CLL has yielded promising results in phase II and III trials (22-24). The combination of rituximab with FC (R-FC regimen) demonstrated particularly high rates of overall response, CR, PFS, and overall survival in previously untreated and relapsed/refractory CLL. In order to validate this concept the German CLL study group (GCLLSG) initiated a multicentre, multinational phase III trial, CLL8, to evaluate the efficacy and tolerability of R-FC versus FC for the first-line treatment of pts with advanced CLL (23). In this study 817 patients were randomly assigned to receive 6 courses of either FC of R-FC. The overall response rate was significantly higher in the R-FC arm (95%) compared to FC (88%) (p = 0.001). The complete response rate of the R-FC arm was 52% as compared to 27.0% in the FC arm (p < 0.0001). PFS was 76.6% at 2 years in the R-FC arm and 62.3% in the FC arm (p < 0.0001). There was a longer OS in the R-FC arm.