BTK and B-cell chronic lymphocytic leukemia: Pirtobrutinib is also highly selective for BTK, with resultant tolerability leading to few discontinuations for adverse events,17 and thus far has favorably low rates of atrial fibrillation when compared with rates seen with covalent BTK inhibitors.27 While the majority of ongoing trials are focusing on CLL/SLL, forthcoming data in MCL may also establish a role for pirtobrutinib in the relapsed/refractory disease setting where progress is greatly needed.