Dao KHT, Gotlib J, Deininger MMN, et al. - Via conducting a phase II study of the JAK1/2 inhibitor ruxolitinib in 44 patients [21 chronic neutrophilic leukemia (CNL) and 23 atypical chronic myeloid leukemia (aCML)], the safety and efficacy of ruxolitinib in patients with CNL and aCML were investigated, irrespective of Colony-stimulating factor-3 receptor (CSF3R) mutation status. As per outcomes, the patients showed good tolerability to ruxolitinib; it exhibited an estimated response rate of 32%. The response was more frequently observed among patients with a diagnosis of CNL and/or harboring CSF3R-T618I.