JAK1 and B-cell chronic lymphocytic leukemia: Ruxolitinib is a JAK1/2 inhibitor approved for the treatment of intermediate or high‐risk myelofibrosis and polycythemia vera after an inadequate response or intolerance to hydroxyurea.8, 9 In CLL, it has relatively weak therapeutic activity and can cause significant anemia and thrombocytopenia as a single agent.10, 11 However, when combined with ibrutinib, it sensitizes CLL cells to cytotoxic drugs in vitro.5