Pirtobrutinib, a Highly Selective, Non-Covalent (Reversible) BTK Inhibitor in Relapsed/Refractory Follicular Lymphoma: Results from the Phase 1/2 BRUIN Study

Nirav N. Shah, Pier Luigi Zinzani, Michael L. Wang, Sunita D. Nasta, Ewa Lech-Maranda, Yoshiaki Ogawa, Bita Fakhri, Bryone Kuss, Kanami Miyashita, Krish Patel, Catherine C. Coombs, Shuo Ma, Manish Patel, Minal A. Barve, Benoit Tessoulin, Anastasios Stathis, Won Seog Kim , Daisuke Ennishi, Daigo Hashimoto, Kensuke KojimaAndrew D. Zelenetz, Jonathon B. Cohen, Julie M. Vose, Kami J. Maddocks, Talha Munir, Fangfang Sun, Faith Bian, Donald E. Tsai, Paolo Abada, Chan Y. Cheah

Research output: Contribution to journalMeeting Abstractpeer-review


Background: Follicular lymphoma (FL) is a chronic and incurable disease requiring multiple lines of therapy for patients (pts) with relapsed/refractory (R/R) disease. Covalent Bruton tyrosine kinase inhibitors (cBTKi) have transformed the management of select B-cell malignancies, in particular chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). However, despite the transformative impact in CLL and MCL, the efficacy of single-agent cBTKi has been limited in pts with R/R FL, with an overall response rate (ORR) of 20.9% to 37.5% (Gopal et al, J Clin Oncol, 2018; Bartlett et al, Blood, 2018). Pirtobrutinib, a highly selective, non-covalent (reversible) BTKi, inhibits both wildtype and C481-mutant BTK with equal low nM potency and has a favorable oral pharmacology that enables continuous BTK inhibition throughout the once-daily dosing interval. Pirtobrutinib has demonstrated promising efficacy and tolerability in pts with poor-prognosis B-cell malignancies following prior therapy, including cBTKi. Here, we report the safety and efficacy of pirtobrutinib in a cohort of pts with R/R FL from the BRUIN study (NCT03740529).

Methods: Pts with previously treated B-cell malignancies were eligible for treatment with pirtobrutinib monotherapy in either the dose escalation or expansion portion of the multicenter phase 1/2 BRUIN study. FL diagnosis required pathologic review of an adequate biopsy. Key endpoints included investigator-assessed ORR per Lugano 2014 criteria, duration of response (DoR), progression-free survival (PFS), overall survival (OS), and safety. A data cutoff date of 05 May 2023 was utilized.

Results: Among the 48 pts with FL, 45 (94%) pts received the recommended phase 2 dose of pirtobrutinib (200 mg once daily) as their starting dose. Pts had a median age of 64.5 years (range, 37.0-85.0), were mostly male (60%, n=29), and had a median of 3 (range, 1-12) prior lines of therapy. Most pts (81%, n=39) had Ann Arbor stage III/IV disease. The Follicular Lymphoma International Prognostic Index (FLIPI) risk was low (0-1) in 9 (19%) pts, intermediate (2) in 13 (27%) pts, high (3-5) in 23 (48%) pts, and missing in 3 (6%) pts. Overall, 43 (90%) pts had received chemotherapy plus an anti-CD20 antibody, 17 (35%) pts had received a PI3K inhibitor, 14 (29%) pts had received lenalidomide, 6 (13%) pts had received an autologous stem cell transplant, and 4 (8%) pts had received CAR T-cell therapy. Of the 4 (8%) pts who had received a prior cBTKi, 3 discontinued due to disease progression and 1 discontinued for intolerance. The ORR was 50.0% (95% confidence interval [CI], 35.2-64.8), including 7 (14.6%) complete responses and 17 (35.4%) partial responses (Figure). An additional 12 (25.0%) pts had stable disease. Among 4 pts who had received prior cBTKi, 3 achieved partial response and 1 had stable disease. With a median follow-up of 18.4 months (interquartile range, 10.1-21.0) among 24 responding pts, median DoR was 5.5 months (95% CI, 3.7-not estimable [NE]), and the 18-month estimated DoR rate was 41.0% (95% CI, 20.1-60.9). Median PFS was 5.8 months (95% CI, 3.8-8.1), and the 18-month estimated PFS rate was 32.3% (95% CI, 19.1-46.2). Median OS was NE, and the 18-month estimated OS rate was 78.3% (95% CI, 62.1-88.1). The efficacy outcomes by FLIPI risk category are presented in the Table. The median time on treatment was 7.6 months (range, 0.6-42.2), with 14 (29.2%) pts still receiving pirtobrutinib. The most frequent treatment-emergent adverse events (TEAEs), regardless of attribution, were diarrhea (29.2%, n=14), fatigue (25.0%, n=12), and nausea (22.9%, n=11). TEAEs of hemorrhage/hematoma (6.3%, n=3), hypertension (4.2%, n=2), and atrial fibrillation/flutter (2.1%, n=1) were infrequent. The most frequent grade ≥3 TEAEs were infection (18.8%, n=9) and neutropenia/neutrophil count decreased (14.6%, n=7). Only 1 (2.1%) pt had a treatment-related adverse event (rash) that led to pirtobrutinib discontinuation.

Conclusions: In this cohort of heavily pre-treated pts with R/R FL, pirtobrutinib showed potential efficacy and was well tolerated, including in pts with high risk FLIPI.
Original languageEnglish
Pages (from-to)3026-3030
Number of pages5
Issue numberSupplement 1
Publication statusPublished - 2 Nov 2023


  • Lymphoma
  • Follicular lymphoma (FL)
  • Inhibitors
  • Pirtobrutinib


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