Bendamustine in Combination with Rituximab (BR) for Patients with Relapsed Chronic Lymphocytic Leukemia (CLL): A Multicentre Phase II Trial of the German CLL Study Group (GCLLSG)
Authors: Fischer Kirsten , Stilgenbauer Stephan , Schweighofer Carmen D , Busch Raymonde , Renschler Jasmin , Kiehl Michael , Balleisen Leopold , Eckart Michael J , Fink Anna- Maria , Kilp Julia , Ritgen Matthias , Böttcher Sebastian , Kneba Michael , Döhner Hartmut , Eichhorst Barbara F , Hallek Michael , Wendtner Clemens- Martin ,   The German CLL Study Group
Published: April 2020

Introduction: Bendamustine, an alkylating agent with additional properties of a purine analogue, has shown considerable activity in monotherapy for solid and lymphoid malignancies including chronic lymphocytic leukemia (CLL). In vitro studies have demonstrated synergistic pro-apoptotic effects of bendamustine and the CD20 antibody rituximab (BR) in primary CLL cells. Encouraging clinical results have been obtained using BR combination treatment in relapsed/refractory and previously untreated Non-Hodgkin’s lymphoma. This phase II trial represents the first study evaluating the efficacy and toxicity of bendamustine in combination with rituximab in patients (pts) with relapsed or refractory CLL.

Patients and Methods: 81 pts with a median number of 2 (1–3) pretreatments were enrolled between March 2006 and June 2007. Patients received 70 mg/m² bendamustine on day 1 and 2 combined with 375mg/m² rituximab for the first cycle and 500 mg/m² for the second and subsequent cycles. BR treatment was administered every 28 days for up to 6 courses. Blood samples were taken for molecular cytogenetics by fluorescence in situ hybridization (FISH) and analysis of the immunoglobulin heavy chain (IgVH) mutational status prior to the first treatment course. Assessment for minimal residual disease (MRD) was performed by four-colour flow cytometry of peripheral blood and bone marrow. Primary endpoint of the trial was the overall response rate (ORR). Secondary endpoints included toxicity, duration of response, event-free survival, MRD response rate and overall response rate in biological defined risk groups.

Results: 81 pts (mean age 66.7 years) received a total of 328 treatment cycles. A mean number of 4.5 courses was administered. In total 123 CTC grade 3/4/5 adverse events were reported, most frequently on myelosuppression and infections: grade 3/4 anemia occurred in 6.1%, grade 3/4 leukopenia/neutropenia and thrombocytopenia in 11.9% and 9.1% of all given courses, respectively. 16 episodes (4.9%) of CTC grade ≥3 infections were documented, most of them could be successfully managed. However, treatment related mortality occurred in 3.7% of pts: three pts died due to severe infections associated with treatment related neutropenia including 1 fatal pneumonia, one sepsis after diagnosis of Richter’s syndrome and 1 urosepsis. In 62 pts data for response assessment were available: 19 pts were not evaluable for response due to withdrawal or missing of consent, violation of enrolment criteria or early discontinuation of therapy. The overall response was 77.4% with complete remissions (CR) in 14.5% (9 pts) and a partial response (PR) in 62.9% of pts (39 pts). An MRD level below 10E-4 was measured after completion of therapy in 2 of 30 evaluable pts in peripheral blood, while none of the pts achieved MRD negativity in bone marrow. Stable disease (SD) was achieved in 17.7% (11 pts) whereas 3 pts (4.8%) had progressive CLL (PD). Differences in response were observed among genetic subgroups: 12 of 13 pts with 11q- achieved a remission with 11 PR and 1 CR (ORR: 92.3%). Accordingly, 8 of 8 patients with +12 responded (7 PR, 1 CR). In the high-risk group with 17p-, four of nine pts showed a partial remission (ORR: 44,4%). 29 of 39 pts (ORR: 74.4%) with unmutated IgVH status were responsive to BR.

Conclusion: Bendamustine plus rituximab is an effective treatment regimen for pts with relapsed and/or refractory CLL and has notable activity in high-risk CLL disease. Major but tolerable treatment toxicities were myelosuppression and infections. Ongoing trial follow-up analysis will define response duration and long-term safety. In a forthcoming trial the German CLL Study group will investigate the efficacy of BR in comparison to fludarabine-based immunochemotherapy (FCR) for first-line treatment of CLL.