Eli Lilly (NYSE: LLY) reported that pirtobrutinib (Jaypirca) added to venetoclax and rituximab produced a statistically significant improvement in progression-free survival over venetoclax and rituximab alone in previously treated chronic lymphocytic leukemia or small lymphocytic lymphoma, marking the fourth positive Phase III readout for the drug in CLL and the first time any BTK inhibitor has outperformed a venetoclax-containing control arm in a randomized Phase III setting.
BRUIN CLL-322 (NCT04965493) is a global, randomized, open-label Phase III study enrolling 639 patients with previously treated CLL/SLL, randomized 1:1 to pirtobrutinib plus venetoclax and rituximab or venetoclax and rituximab alone, with treatment in both arms capped at two years.
The trial met its primary endpoint of progression-free survival as assessed by blinded independent review committee, with the improvement consistent across subgroups and regardless of prior covalent BTK inhibitor exposure. Overall survival, a key secondary endpoint, was not mature at this analysis but trended in favor of the pirtobrutinib arm. No numerical data — hazard ratios, median PFS values, or response rates — were disclosed in the topline release; Lilly said full results will be presented at a medical congress and submitted for peer review. Adverse event rates were similar across arms, with low rates of treatment discontinuation in both groups, consistent with the established safety profiles of each component.
The development context
The absence of quantitative data limits clinical interpretation for now, but the trial's design carries weight independent of the magnitude of effect. Venetoclax plus rituximab, approved in 2018 for relapsed or refractory CLL as a time-limited 24-month regimen, has become a standard second-line option, particularly for patients and clinicians who prefer a fixed-duration approach over continuous BTK inhibitor therapy. Using that regimen as the control arm — rather than a comparator already known to be inferior — raises the evidentiary bar considerably. That BRUIN CLL-322 cleared it positions pirtobrutinib as a potential triplet backbone for second-line CLL rather than simply an alternative to existing options.
The trial's enrollment profile adds further clinical relevance. The population was predominantly composed of patients previously treated with covalent BTK inhibitors — ibrutinib, acalabrutinib, or zanubrutinib — reflecting a patient group that has grown substantially as first-line BTK inhibitor use has expanded. Covalent BTK inhibitors bind irreversibly to cysteine-481 on BTK, and resistance frequently emerges through the C481S substitution, which abolishes covalent binding. Pirtobrutinib binds BTK non-covalently and reversibly, retaining activity against C481S-mutant BTK and forming the pharmacological basis for its use in the post-covalent BTKi setting. The drug already carries FDA approval for relapsed or refractory CLL/SLL in patients previously treated with a covalent BTK inhibitor, as well as for relapsed or refractory mantle cell lymphoma.