BRUIN MCL-321: phase III study of pirtobrutinib versus investigator choice of BTK inhibitor in BTK inhibitor naive mantle cell lymphoma

Treatment with covalent Bruton tyrosine kinase inhibitors (BTKi) represents an important advance in the management of relapsed or refractory mantle cell lymphoma, but these treatments are not curative and many patients ultimately relapse. Pirtobrutinib, a highly selective, non covalent (reversible) BTKi, inhibits both wild type and C481-mutant BTK with equal low nM potency, and has favorable oral pharmacology that enables continuous BTK inhibition throughout the dosing interval regardless of intrinsic rate of BTK turnover. Pirtobrutinib is well tolerated and has demonstrated promising efficacy in patients with poor prognosis B-cell malignancies following prior therapy, including covalent BTKi. This phase III, head-to-head, randomized study (NCT04662255) will evaluate whether pirtobrutinib is superior to investigator's choice of covalent BTKi in patients with previously treated, BTKi-naive mantle cell lymphoma.MCL is an uncommon type of B-cell non-Hodgkin lymphoma, a cancer of the immune system. It starts in the part of the lymph node called the mantle zone, where unusual B cells gather and crowd out healthy B cells in the lymph nodes, spleen, bone marrow and/or other organs. MCL can be caused by inappropriate cell signaling. BTK has been identified as a key driver of unusual cell signaling and blocking BTK has been shown to help kill the cancer cells. Covalent (not reversible) BTK inhibitors have advanced the treatment of MCL, but the effectiveness of these treatments is limited by side effects and treatment resistance. Pirtobrutinib, a non covalent (reversible) BTK inhibitor, has been shown to have manageable side effects and to be effective in patients with MCL following previous treatment, including treatment with covalent BTK inhibitors. The BRUIN MCL-321 study compares pirtobrutinib with three currently approved covalent BTK inhibitors (ibrutinib, acalabrutinib or zanubrutinib), in patients with MCL who have never received any form of BTK inhibitor. This trial will look at how many people live with the disease without it getting worse. Like other cancer treatments, pirtobrutinib may affect both healthy cells and tumor cells, which can result in side effects that will also be looked at in this study. This study is active and currently recruiting new patients who have received at least one previous therapy for MCL and have never been treated with a BTK inhibitor.