Background
Phase III, open-label, randomized trial (BRUIN CLL-313). 282 previously untreated CLL/SLL patients without del(17p), stratified by IGHV mutation status and Rai stage. Pirtobrutinib is a highly selective, noncovalent (reversible) BTK inhibitor designed to overcome covalent BTKi resistance and offer a differentiated safety profile. Bendamustine + rituximab (BendaR) was the comparator representing standard frontline chemoimmunotherapy. Crossover was permitted at progression; 52.9% of BendaR patients crossed over to pirtobrutinib.
Interventions and follow up
Arm A: Pirtobrutinib monotherapy (continuous, dose per protocol)
Arm B: Bendamustine 90 mg/m² D1–2 + rituximab 375 mg/m² C1 then 500 mg/m² x 6 cycles
Primary endpoint: IRC-assessed progression-free survival (PFS)
mFollow up: 32 months
Arm B: Bendamustine 90 mg/m² D1–2 + rituximab 375 mg/m² C1 then 500 mg/m² x 6 cycles
Primary endpoint: IRC-assessed progression-free survival (PFS)
mFollow up: 32 months
Results
PFS (IRC): HR 0.199, 95% CI 0.107–0.367, P<.0001
24-month PFS rate: 93.4% vs 70.7%
PFS (investigator): HR 0.186, 95% CI 0.093–0.371
OS (interim): HR 0.257, 95% CI 0.070–0.934 — despite 52.9% crossover rate
24-month PFS rate: 93.4% vs 70.7%
PFS (investigator): HR 0.186, 95% CI 0.093–0.371
OS (interim): HR 0.257, 95% CI 0.070–0.934 — despite 52.9% crossover rate
Adverse events
Overall toxicity: Grade ≥3 TEAEs 40.0% (pirtobrutinib) vs 67.4% (BendaR)
Tolerability: Dose reductions 3.6% vs 31.1%; discontinuation due to TEAEs 4.3% vs 15.2%; consistent with the known pirtobrutinib safety profile
Tolerability: Dose reductions 3.6% vs 31.1%; discontinuation due to TEAEs 4.3% vs 15.2%; consistent with the known pirtobrutinib safety profile
Conclusions
Pirtobrutinib demonstrated superior PFS over BendaR in treatment-naive CLL/SLL, with a substantially more favorable tolerability profile. OS trends favored pirtobrutinib despite protocol-allowed crossover.
Key Limitations
BendaR is not a preferred frontline regimen for CLL in current practice (cBTKi or venetoclax-obinutuzumab are standard), so the comparator arm may underrepresent the current standard of care. Open-label design. Del(17p) patients excluded. Crossover dilutes the OS signal. Relatively short median follow-up of 32 months limits long-term OS assessment.
Clinical Context
Pirtobrutinib joins the frontline CLL landscape alongside covalent BTKi monotherapy (ibrutinib, acalabrutinib, zanubrutinib) and venetoclax-based fixed-duration regimens. FDA approved pirtobrutinib for post-cBTKi CLL/SLL; frontline approval is pending these data. ESMO and ASCO frameworks favor BTKi or venetoclax-based approaches in untreated CLL without del(17p).