ATLANTA—Rituximab-bendamustine showed significantly higher rates of complete response (CR) vs rituximab-chlorambucil among patients with chronic lymphocytic leukemia (CLL) ineligible for a fludarabine-containing standard-of-care regimen, according to interim results of the phase 3b MaBLe study presented during the 54th American Society of Hematology Annual Meeting and Exposition.

However, both regimens, “could provide useful treatment options” for this population, noted Veronique Leblond, MD, PhD, Hematology, Hôpital Pitié-Salpêtrière, Paris, France, and colleagues.

The ongoing MaBLe study is assessing confirmed CR rates after 6 cycles of first-line or second-line treatment with the two regimens in patients with CLL.

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In the rituximab-bendamustine arm, patients received six 28-day cycles of bendamustine (first-line, 90mg/m2 Days 1 and 2 and second-line, 70mg/m2 Days 1 and 2) with rituximab 375mg/m2 administered on Day 1 of cycle 1 and rituximab 500mg/m2 cycles 2-6.

Patients in the rituximab-chlorambucil arm received the same dose of rituximab with chlorambucil 10mg/m2 days 1–7, cycles 1–6; if they did not achieve a CR after 6 cycles, they continued to receive chlorambucil monotherapy for up to 6 additional cycles. Tumor assessments were made after cycles 3, 6, and 12 and then every 3 months for at least a year.

To date, 358 patients have been randomly assigned; 126 are included in the interim analysis and others are continuing on study. Median age was 74 years and the majority of patients were taking concomitant medication, 98% in the rituximab-bendamustine arm and 94% in the rituximab-chlorambucil arm. Eighty-five patients were treatment-naïve; 41 had received 1 previous line of treatment.

“Compared with previous clinical trials in CLL where patients are usually younger and fitter, this patient population is closer in age and fitness to patients presenting in the clinic,” Dr. Leblond noted.

After 6 cycles, 14 of 58 patients (24%) in the rituximab-bendamustine arm and 7 of 68 patients (10%) in the rituximab-chlorambucil arm had a confirmed CR (P=0.033). For first-line patients, corresponding CR rates were 30% in the rituximab-bendamustine arm vs 13% in the rituximab-chlorambucil arm (P=0.054); for second-line patients, these rates were 11% vs 4%, respectively (P=0.413).

Overall response rate (ORR) did not differ between the arms: 88% in the rituximab-bendamustine arm and 81% in the rituximab-chlorambucil arm (P=0.404). For first-line patients, ORRs were 88% vs 80% and, for second-line patients, 89% vs 83%, respectively.

Safety was similar between the two treatment arms; the most common grade ≥3 adverse events (AEs) were neutropenia, leukopenia and lymphopenia. Five patients (9%) in the rituximab-bendamustine arm and 8 patients (12%) in the rituximab-chlorambucil arm withdrew from the study prematurely due to AEs. Seven deaths were determined to be AE-related (two patients in the rituximab-bendamustine study arm and five patients in the rituximab-chlorambucil arm).