Ruxolitinib Phosphate in Treating Patients With Chronic Neutrophilic Leukemia or Atypical Chronic Myeloid Leukemia

PRIMARY OBJECTIVES: I. To determine the proportion of patients with chronic neutrophilic leukemia (CNL) and atypical chronic myeloid leukemia (aCML) who have a hematologic response to ruxolitinib (ruxolitinib phosphate) (partial response \[PR\], complete response \[CR\], complete response, partial \[CRp\]). SECONDARY OBJECTIVES: I. To determine the frequency of grade 3 or 4 hematologic and non-hematologic adverse events experienced by subjects during therapy with ruxolitinib. II. To determine whether hematologic responses correlate with certain types of mutations in colony stimulating factor 3 receptor (CSF3R) and reduction in mutant CSF3R allele burden in the peripheral blood. III. To determine the maximum clinical responses for each subject and the median duration of maximum clinical responses. IV. To determine the mean % reduction of spleen size, estimated by volume using the conventional prolate ellipsoid method as measured by ultrasound compare to baseline. V. To determine the mean % reduction of total symptom score as measured by a modified Myeloproliferative Neoplasm Symptom Assessment Form version 2.0 (MPN-SAF) compared to start of study (day 1, cycle 1). VI. To determine overall survival in subjects who complete a minimum of 1 dose of study drug. VII. To determine the proportion of subjects who discontinue after completion of \> 3 cycles but \< 6 cycles. VIII. To determine the proportion of subjects who discontinue prior to completion of cycle 3. OUTLINE: Patients receive ruxolitinib phosphate orally (PO) every other day, once daily (QD), or twice daily (BID) on days 1-28. Each patient will be followed for a maximum of 96 weeks (24 cycles, 1 cycle is 4 weeks long). If the study drug continues to be effective, the patient may be eligible to continue on study drug past 24 cycles. After completion of study treatment, patients are followed up within 2 weeks and at 4-6 weeks.