Safety and Efficacy of Acalabrutinib Plus Venetoclax and Rituximab in Patients with Treatment-Naïve (TN) Mantle Cell Lymphoma (MCL)

ABSTRACT

Background: First-line conventional chemoimmunotherapy in MCL can be improved. Promising results have been seen with Bruton tyrosine kinase inhibitors (BTKis) in combination with venetoclax (V) and an anti-CD20 monoclonal antibody in patients (pts) with relapsed/refractory or TN MCL. Acalabrutinib (A) is a next-generation, highly selective, covalent BTKi currently approved for relapsed/refractory MCL. We report initial safety and efficacy results of the ongoing, multicenter, open-label phase 1b study of A, V, and rituximab (R) (AVR) in TN MCL. Methods: TN MCL pts aged ≥18 y with ECOG PS ≤2 were eligible. Starting on cycle 1 day 1, A was administered at 100 mg BID until disease progression or discontinuation for other reasons. R was administered at 375 mg/m 2 on day 1 of each 28-day cycle for 6 cycles, followed by maintenance every other cycle for pts achieving complete response (CR) or partial response (PR), through cycle 24. Starting on cycle 2 day 1, V was administered via an initial 5-wk ramp-up schedule (20, 50, 100, 200, and 400 mg/d) to 400 mg/d, through cycle 25. Dose-limiting toxicity (DLT) was assessed from cycle 2 day 1 to cycle 3 day 28. Primary endpoint was AVR safety. Secondary endpoints were overall response rate (ORR), duration of response (DOR), and progression-free survival (PFS) per Lugano criteria. Positron-emission tomography (PET)/computed tomography (CT) scans were performed after 3 and 6 cycles and to confirm CR at any time. CT scans were performed after 3, 6, 9, and 12 cycles, and then every 6 cycles. Longitudinal minimal residual disease (MRD) was assessed using the clonoSEQ assay in peripheral blood at PR, CR, every 6 cycles post-CR, and treatment end. Results: 21 pts were enrolled (median age 66 y [range 51-85];ECOG PS ≤1 20 [95%];Ann Arbor stage IV disease 19 [90%];bulky disease >5 cm 7 [33%];intermediate- and high-risk simplified MCL International Prognostic Index scores 11 [52%] and 4 [19%], respectively;blastoid variant 1 [5%];and Ki-67 proliferation index ≥50% 3 [14%]). Fifteen (71%) pts had bone marrow (BM) involvement at baseline. As of March 19, 2021, median time on study was 16 mo (range 8-26.2). Median (range) number of cycles administered was 15 (7-27) for A, 13.5 (5-23) for 400 mg daily V, and 12 (6-15) for R. Seventeen (81%) pts remain on study treatment and 4 (19%) have discontinued (progressive disease n=1;COVID-19 infection n=3). No DLTs were observed;V 400 mg daily after ramp-up was the dose chosen for triple therapy. Most common any-grade AEs in ≥20% of pts were diarrhea (13 [62%]), headache (11 [52%]), fatigue (10 [48%]), neutropenia (6 [29%]), paresthesia (6 [29%]), cough (6 [29%]), dyspnea (6 [29%]), myalgia (5 [24%]), dizziness (5 [24%]), and hypoesthesia (5 [24%]). Grade 3/4 AEs in ≥2 pts were neutropenia (5 [24%]) and pneumonia (2 [10%]). Serious any-grade AEs in ≥2 pts were COVID-19 infection (4 [19%]) and pneumonia (2 [10%]). In the 4 pts with COVID-19 infection, the events led to triple-drug discontinuation and death in 3 pts and to dose holds of A and V and event resolution in 1 pt (all considered unrelated to study treatment). Diarrhea led to V dose reduction in 1 pt. AEs led to dose holds in 12 (57%) pts and were associated with A, V, and R in 52%, 48%, and 14%, respectively. Events of clinical interest are shown in Table 1. At the end of cycle 6, ORR was 100%, with CR/PR in 90%/10% by PET/CT alone (11 of the 13 CRs by PET/CT lacked BM confirmation);the CR/PR rate by Lugano criteria with BM confirmation was 38%/62% (Table 2). Median DOR was 19 mo (95% CI 17-not estimable [NE]) overall, and not reached when the 3 pts with COVID-19 deaths were censored. Median PFS and OS were not reached. The 1-y PFS and OS rates were 89% (95% CI 62-97) and 95% (95% CI 71-99), respectively. Treating the 3 COVID-19 deaths as censored, the 1-y PFS rate was 93.8% (95% CI 63.2-99.1). Median time to initial response and best response was 2.8 mo. Twelve of 16 (75%) pts with available MRD results at cycle 6 achieved MRD negativity (10 -6), including 6 pts with