Bendamustine, Obinutuzumab and Venetoclax As Induction Therapy for Untreated Mantle Cell Lymphoma

Bendamustine-rituximab (BR) is a standard of care for patients with mantle cell lymphoma (MCL) with median progression free survival (PFS) of approximately 3 years. Venetoclax has proven activity both as a single agent and in combination with other targeted therapies in relapsed MCL. We developed a phase 2 study of bendamustine, obinutuzumab, and venetoclax (BOV) for untreated patients with MCL to determine the efficacy and toxicity of this combination (NCT03872180).

Patients ≥ 18 years old with untreated MCL received up to six 28-day cycles of BOV, consisting of bendamustine (90mg/m² on D1-2) and obinutuzumab (1000mg, C1: D 1,8,15 and C2-6: D1) with a venetoclax ramp up from 20mg to 200mg during the first cycle and then 400mg on days 1-10 of cycles 2-6. Post-induction therapy is determined by the treating physician and is not dictated by the study. The primary endpoint was CR rate at the end of induction, per Lugano criteria. We assumed a historical CR rate of 60% with BR, with a goal CR rate of 85% with the BOV regimen and plan to accrue 23 total patients to assess for this difference. This was a two-stage design that included 9 patients in stage 1 with a requirement of 7 CR's in the first 9 patients to justify continued accrual. Secondary and correlative endpoints include PFS/overall survival, toxicity (including frequency and severity of tumor lysis syndrome), and MRD negativity using both commercial IgHTS assays as well as CAPP-Seq. Supportive care included G-CSF, antimicrobial prophylaxis, and prescribed monitoring for and management of tumor lysis syndrome.

11 patients have initiated therapy. Median age is 70 years (45-80), with 7 males and 4 females. All 11 patients had marrow involvement. Five patients had Ki67 index ≥30%, and TP53/17p abnormalities were found in 2 patients. Eight patients have completed 6 cycles, one patient discontinued study therapy after 5 cycles due to thrombocytopenia and 2 patients remain on therapy after 5 cycles of treatment. Of 9 patients who have completed end of treatment restaging, the ORR was 100%, including 8 CR's (89%) and 1 PR. The two patients currently completing study therapy have completed their interim PET/CT's and both have achieved CR. Three patients experienced grade 3+ obinutuzumab infusion reactions on cycle 1 day 1, with both patients requiring admission but subsequently fully recovering. One of these patients chose to forgo additional obinutuzumab while a second patient safely completed 6 cycles of treatment. The third patient initiated treatment in the hospital and experienced atrial fibrillation requiring ICU transfer, as well as grade 2 hyperkalemia while receiving day 1 treatment. Cardiology did not feel AFib was a result of TLS. She was ultimately able to safely complete 6 cycles of obinutuzumab. Although this event was not clear clinical TLS, the protocol was subsequently amended to incorporate venetoclax administration beginning on day 8 of cycle 1 to prevent overlapping infusional and TLS toxicities from venetoclax and obinutuzumab on day 1. No other patients have had TLS to date. Grade 3/4 hematologic toxicities include neutropenia (n=4), anemia (n=1), thrombocytopenia (n=4) leukopenia (n=3), and lymphopenia (n=10). Grade 3/4 non-hematologic toxicities included rash (n=2), hypophosphatemia (n=2). One patient has experienced prolonged leukopenia 2 months after finishing 6 cycles of therapy and was unable to collect stem cells after cycle 4 for a planned post-induction autologous transplant. To date, 2 patients have relapsed at 7 and 8 months after completing therapy, and one patient died suddenly while in remission of unknown causes at 6 months post-treatment. Of the two relapses, one patient chose not to receive any obinutuzumab during treatment due to a grade 3 reaction during cycle 1, and both patients initially presented with aggressive leukemic phase disease with Ki67 > 30%.

Here we report the pre-planned stage 1 of this phase 2 study, the BOV regimen has resulted in CRs in 8 of the first 9 patients, and accrual continues to stage 2. Expected hematologic and infusional toxicities have been manageable. One patient has discontinued therapy due to toxicity, and the prescribed venetoclax ramp-up has successfully avoided clinically significant tumor lysis syndrome. Accrual continues, and additional follow-up of currently treated patients will provide insights into response duration, OS, and rate of MRD negativity with this regimen.