Activity of Ruxolitinib in Chronic Neutrophilic Leukemia and Atypical Chronic Myeloid Leukemia

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In a phase II study reported in the Journal of Clinical Oncology, Dao et al found that the JAK1/2 inhibitor ruxolitinib was active in patients with chronic neutrophilic leukemia (CNL), with less activity observed in those with atypical chronic myeloid leukemia (CML) and greater activity observed among those with the activating colony-stimulating factor-3 receptor (CSF3R) T618I mutation.

Study Details

In total, 43 evaluable patients—including 20 with CNL and 23 with atypical CML—were enrolled into the trial irrespective of CSF3R mutation status. The primary outcome measure was hematologic response rate by the end of six continuous 28-day cycles for the first 25 patients enrolled. CSF3R membrane-proximal and transmembrane mutations were present in 76% of patients with CNL and 26% of those with atypical CML.



  • Response was observed in 32% of the first 25 patients, including 58% of patients with CNL and 8% with atypical CML.
  • Response was observed in 54% of patients with a CSF3R mutation vs 8% of those with wild-type CSF3R.

Among the first 25 patients, the overall response rate was 32% (eight partial responses). Response rates were 58% (7 of 12 patients) in the CNL group and 8% (1 of 13 patients) in the atypical CML group, and 54% (7 of 13 patients) among patients with a CSF3R mutation and 8% (1 of 12 patients) among those with wild-type CSF3R.

Among the total of 43 evaluable patients, the response rate was 35%, consisting of nine partial responses and four complete responses among patients with CNL and two partial responses in patients with atypical CML. CSF3R mutation was present in 50% of responders.  

Adverse Events

Grade ≥ 3 nonhematologic adverse events were observed in 55% of patients, with the most common being fatigue, lung infection, and pneumonitis (9% each). Grade 3 or 4 anemia and thrombocytopenia occurred in 34% and 14% of patients, respectively. No treatment-related serious adverse events were observed.

The investigators concluded, “Ruxolitinib was well tolerated and demonstrated an estimated response rate of 32%. Patients with a diagnosis of CNL and/or harboring CSF3R T618I were most likely to respond.”

Kim-Hien T. Dao, DO, PhD, of Oregon Health & Science University, Portland, is the corresponding author for the Journal of Clinical Oncology article.

Disclosure: The study was supported by Incyte Corporation. For full disclosures of the study authors, visit

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