The role of the monoclonal anti-CD20 antibodies for treatment of patients with chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is a malignant disease and accounts for 25% of all leukaemias. The disease is the most common lymphoid malignancy in western countries, and is characterised by a highly variable clinical course and prognosis. Some patients may have minimal or no symptoms for many years with a normal life expectancy, without requiring treatment. Other people are symptomatic at diagnosis or soon thereafter and can experience infectious and autoimmune complications, leading to a reduced lifespan. Standard treatment includes chemotherapy with one or more agents. Presently monoclonal antibodies are added, especially alemtuzumab and rituximab. However, the impact of these agents remains unclear, as there have been hints for increased overall survival, but also for an increased risk of severe infections in non-randomised trials. In this systematic review we summarised and analysed the evidence from randomised controlled trials on efficacy and safety of monoclonal anti-CD20 antibodies (such as rituximab and ofatumumab) in the treatment of CLL. We searched medical databases, such as EMBASE, MEDLINE and CENTRAL, and found seven randomised controlled trials fulfilling our inclusion criteria. Included trials compared anti-CD20 antibodies, particularly rituximab, to no further therapy or compared to anti-cancer therapy in CLL, irrespective of whether the patients were newly diagnosed or relapsed patients. Only five of the seven identified trials could be included in one of the two performed meta-analyses.

Three trials (N = 1421) were included in the meta-analysis assessing the efficacy of chemotherapy plus rituximab compared to chemotherapy without further therapy. The meta-analysis showed for patients receiving additional rituximab a statistically significant improvement of overall survival and a longer time without progression of the disease. Treatment with rituximab caused more adverse events, but this did not lead to a statistically significant difference regarding death caused by treatment. However, patients who were treated within these trials did not suffer from other severe health problems aside from CLL; therefore, it remains unclear whether patients with severe co-morbidities will benefit from this treatment option.

In summary, this meta-analysis showed that patients receiving chemotherapy plus rituximab benefited in terms of survival compared to those with chemotherapy alone. Therefore, it supports the recommendation of rituximab in combination with fludarabine and cyclophosphamide as an option for the first-line treatment as well as for people with relapsed or refractory CLL. Further research should focus on the evaluation of benefits of adding rituximab to other chemotherapy regimens than fludarabine with cyclophosphamide in the therapy of previously untreated, relapsed or refractory patients. It should also assess whether patients with serious co-morbidities will benefit from the addition of rituximab to chemotherapy.

The available evidence regarding assessed comparisons from four other trials was not sufficient to deduct final conclusions.Two trials evaluated polychemotherapy in combination with rituximab versus alemtuzumab respectively. One trial evaluated two different rituximab schedules: rituximab given concurrently with primary treatment plus rituximab therapy given subsequently to the primary treatment versus primary treatment alone with subsequent administration of rituximab. One trial investigated two different dosages (500 mg and 1000 mg) of ofatumumab in addition to fludarabine with cyclophosphamide.

Randomised Controlled Trials (RCTs) are needed to determine the clinical effects of novel anti-CD20 antibodies, such as ofatumumab or GA101, compared to rituximab. We are aware of 16 ongoing studies, including three trials comparing ofatumumab with or without additional chemotherapy versus no treatment. The findings of these trials will be included in an update of this review and could lead to different conclusions and may allow a judgement on general efficacy and safety of monoclonal anti-CD20 antibody in the treatment of CLL.

Authors' conclusions: 

This meta-analysis showed that patients receiving chemotherapy plus rituximab benefit in terms of OS as well as PFS compared to those with chemotherapy alone. Therefore, it supports the recommendation of rituximab in combination with FluC as an option for the first-line treatment as well as for the people with relapsed or refractory CLL. The available evidence regarding the other assessed comparisons was not sufficient to deduct final conclusions.

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Background: 

Chronic lymphocytic leukaemia (CLL) accounts for 25% of all leukaemias and is the most common lymphoid malignancy in western countries. Standard treatments include mono- or polychemotherapies, usually combined with monoclonal antibodies such as rituximab or alemtuzumab. However, the impact of these agents remains unclear, as there are hints for increased risk of severe infections.

Objectives: 

The objectives of this review are to provide an evidence-based answer regarding the clinical benefits and harms of monoclonal anti-CD20 antibodies (such as rituximab, ofatumumab, GA101) compared to no further therapy or to other anti-leukaemic therapies in patients with CLL, irrespective of disease status.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 12, 2011), MEDLINE (from January 1990 to 4 January 2012), and EMBASE (from 1990 to 20 March 2009) as well as conference proceedings (American Society of Hematology, American Society of Clinical Oncology, European Hematology Association and European Society of Medical Oncology) for randomised controlled trials (RCTs).

Selection criteria: 

We included RCTs examining monoclonal anti-CD20 antibodies compared to no further therapy or to anti-leukaemic therapy such as chemotherapy or monoclonal antibodies in patients with newly diagnosed or relapsed CLL.

Data collection and analysis: 

We used hazard ratios (HR) as effect measures for overall survival (OS), progression-free survival (PFS) and time to next treatment, and risk ratios (RR) for response rates, treatment-related mortality (TRM) and adverse events (AEs). Two review authors independently extracted data and assessed quality of trials.

Main results: 

We screened a total of 1150 records. Seven RCTs involving 1763 patients were identified, but only five could be included in the two separate meta-analyses we performed. We judged the overall the quality of these trials as moderate to high. All trials were randomised and open-label studies. However, two trials were published as abstracts only, therefore we were unable to assess the potential risk of bias for these trials in detail.

Three RCTs (N = 1421) assessed the efficacy of monoclonal anti-CD20 antibodies (i.e. rituximab) plus chemotherapy compared to chemotherapy alone. The meta-analyses showed a statistically significant OS (HR 0.78, 95% confidence interval (CI) 0.62 to 0.98, P = 0.03, the number needed to treat for an additional beneficial effect (NNTB) was 12) and PFS (HR 0.64, 95% CI 0.55 to 0.74, P < 0.00001) advantage for patients receiving rituximab. In the rituximab-arm occurred more AEs, World Health Organization (WHO) grade 3 or 4 (3 trials, N = 1398, RR 1.15, 95% CI 1.08 to 1.23, P < 0.0001; the number needed to harm for an additional harmful outcome (NNTH) was 9), but that did not lead to a statistically significant difference regarding TRM (3 trials, N = 1415, RR 1.19, 95% CI 0.70 to 2.01, P = 0.52).

Two trials (N = 177) evaluated rituximab versus alemtuzumab. Neither study reported OS or PFS. There was no statistically significant difference between arms regarding complete response rate (CRR) (RR 1.21, 95% CI 0.94 to 1.58, P = 0.14) or TRM (RR 0.31, 95% CI 0.06 to 1.51, P = 0.15). However, the CLL2007FMP trial was stopped early owing to an increase in mortality in the alemtuzumab arm. More serious AEs occurred in this arm (43% with alemtuzumab versus 22% with rituximab; P = 0.006).

Two trials assessed different dosages or time schedules of monoclonal anti-CD20 antibodies. One trial (N = 104) evaluated two different rituximab schedules (concurrent arm: fludarabine plus rituximab (Flu-R) plus rituximab consolidation versus sequential arm: fludarabine alone plus rituximab consolidation). The comparison of the concurrent versus sequential regimen of rituximab showed a statistically significant difference of the CRR with 33% in the concurrent-arm and 15% in the sequential-arm (P = 0.04), that did not lead to statistically significant differences regarding OS (HR 1.14, 95% CI 0.20 to 6.65, P = 0.30) or PFS (HR 0.96, 95% CI 0.43 to 2.15, P = 0.11). Furthermore results showed no differences in occurring AEs, except for neutropenia, which was more often observed in patients of the concurrent arm. The other trial (N = 61) investigated two different dosages (500 mg and 1000 mg) of ofatumumab in addition to FluC. The arm investigating ofatumumab did not assess OS and a median PFS had not been reached owing to the short median follow-up of eight months. It showed no statistically significant differences between arms regarding CRR (32% in the FCO500 arm versus 50% in the FCO1000 arm; P = 0.10) or AEs (anaemia, neutropenia, thrombocytopenia).

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