Background
Phase 3, open-label, randomized controlled trial (BRUIN CLL-321). N=238 patients with R/R CLL/SLL previously treated with a covalent BTK inhibitor (ibrutinib or acalabrutinib). Randomized 1:1 to pirtobrutinib vs investigator's choice of idelalisib + rituximab or bendamustine + rituximab. This is the registrational phase 3 trial for pirtobrutinib in BTKi-pretreated CLL. Published JCO 2025.
Interventions and follow up
Arm A: Pirtobrutinib 200 mg PO once daily until progression or unacceptable toxicity
Arm B: Investigator's choice: idelalisib 150 mg PO twice daily + rituximab; OR bendamustine 70 mg/m² days 1–2 + rituximab (BR) × 6 cycles
Primary endpoint: PFS (independent review)
Median follow-up: ~18 months
Arm B: Investigator's choice: idelalisib 150 mg PO twice daily + rituximab; OR bendamustine 70 mg/m² days 1–2 + rituximab (BR) × 6 cycles
Primary endpoint: PFS (independent review)
Median follow-up: ~18 months
Results
mPFS (pirtobrutinib vs control): 14.0 vs 8.7 months, HR 0.54, P<.001
ORR: 60% vs 39%
mDOR: Not reached vs 9.5 months
OS: No significant difference (crossover permitted, immature)
Subgroups: PFS benefit consistent including venetoclax-pretreated patients
ORR: 60% vs 39%
mDOR: Not reached vs 9.5 months
OS: No significant difference (crossover permitted, immature)
Subgroups: PFS benefit consistent including venetoclax-pretreated patients
Adverse events
Hematologic: Grade ≥3 neutropenia 25% (pirtobrutinib) vs 35% (control); overall grade ≥3 AEs 56% vs 66%
Cardiovascular: AFib any grade 3% (pirtobrutinib) — markedly lower than historical covalent BTKi rates
GI / infections: Diarrhea grade ≥3 1% vs 13% (idelalisib colitis); grade ≥3 infections 15% vs 21%
Discontinuation due to AEs: 12% vs 23%
Cardiovascular: AFib any grade 3% (pirtobrutinib) — markedly lower than historical covalent BTKi rates
GI / infections: Diarrhea grade ≥3 1% vs 13% (idelalisib colitis); grade ≥3 infections 15% vs 21%
Discontinuation due to AEs: 12% vs 23%
Conclusions
Pirtobrutinib significantly improved PFS versus idelalisib + rituximab or BR in BTKi-pretreated R/R CLL/SLL (HR 0.54), with higher ORR and a superior safety profile, including low AFib and fewer discontinuations. This confirms pirtobrutinib as standard of care for patients who have progressed on or are intolerant of covalent BTKi therapy.
Key Limitations
The composite control arm (investigator's choice) limits interpretation — venetoclax-based therapy is a more relevant comparator than idelalisib + rituximab or BR in contemporary practice. Median PFS of 14 months, while statistically superior, remains short in an incurable disease; deeper responses and higher uMRD may be needed for durable control. Venetoclax re-treatment after pirtobrutinib progression is not defined. OS data immature with crossover.
Clinical Context
BRUIN CLL-321 confirmed the FDA approval of pirtobrutinib for R/R CLL/SLL after prior covalent BTKi and a BCL2 inhibitor. Pirtobrutinib is now the preferred option for BTKi-pretreated CLL. For triple-refractory (BTKi + venetoclax + anti-CD20) patients, lisocabtagene maraleucel (TRANSCEND CLL 004) and clinical trials remain options. Combination strategies with pirtobrutinib + venetoclax are under investigation. ESMO-MCBS: not yet assigned.