Abstract The hematopoietic cell kinase (HCK) regulates BTK activation and represents a potential therapeutic target in Waldenstrom macroglobulinemia (WM). We investigated dasatinib, a potent HCK inhibitor, in patients with WM progressing on ibrutinib. Study treatment consisted of dasatinib administered at 100 mg by mouth once daily in four‐week cycles for up to 24 cycles. This study was registered under ClinicalTrials.Gov ID NCT04115059. Three participants were enrolled and received at least one cycle of dasatinib. The best response was stable disease. Two patients received 5 months and one patient received 1 month of therapy. The dose of dasatinib was decreased in one participant due to volume overload. Based on the lack of responses observed, the study was terminated. Dasatinib might not be effective in patients with WM progressing on ibrutinib.
