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

Inclusion Criteria:

* Subjects must be newly diagnosed or previously diagnosed with CNL or aCML; all patients must have a bone marrow biopsy completed during the screening or baseline period if one has not been done within 90 days of day 1, cycle one
* Subjects must have platelet count greater than 25,000 per microliter at baseline and at the start of study (day 1, cycle 1) visit
* Subjects must be able to discontinue any drug treatment aimed at lowering disease burden in CNL or aCML; subjects should discontinue hydroxyurea to treat underlying CNL or aCML disease no later than day -7 (one week before starting ruxolitinib); for drugs that have more long-lasting effects on the marrow, such as thalidomide and its analogs, and interferon, subjects should discontinue these no later than day -28
* Subjects must be willing to accept/continue transfusions to treat low hemoglobin levels
* Subjects must have a life expectancy of \> 6 months

Exclusion Criteria:

* Subjects unable to review and sign informed consent form
* Females who are pregnant or breastfeeding, and males and females who cannot comply with requirements to avoid fathering a child or becoming pregnant
* Subjects with known diagnosis of human immunodeficiency virus (HIV) or chronic active Hepatitis B or C; viral testing is not required; subjects with a history of Hepatitis B and/or C are allowed on trial if the virus is undetected at the time of enrollment
* Subjects with inadequate liver (alanine aminotransferase \[ALT\]/serum glutamate pyruvate transaminase \[SGPT\] above 4 X upper limit of normal \[ULN\] or direct bilirubin 4 X ULN AND the lab abnormalities are felt to be due to underlying liver dysfunction)
* Subjects with end stage renal function (creatinine clearance \[CrCl\] \< 15 mL/min or glomerular filtration rate \[GFR\] \<15 mL/min) regardless of whether hemodialysis is required
* Subjects with clinically serious infections requiring ongoing antibiotic therapy
* Subjects with severe (immediately life threatening) and recent (occurring within the last 3 months) cardiac dysfunction, pulmonary dysfunction, esophageal variceal bleeding, hemorrhagic strokes, or intracranial hemorrhage are not eligible for study participation
* Subjects requiring therapeutic doses of anticoagulation or anti-platelet therapies (aspirin above 81 mg daily, Plavix or similar agents) AND platelet counts are below 50,000 on two different laboratory evaluations, separated by minimum of two weeks
* Taking investigational or commercial agents or therapies with the intent to treat the subject's malignancy other than those therapies permitted
* Subjects with invasive malignancy over the previous 2 years except treated early stage carcinomas of the skin, completely resected intraepithelial carcinoma of the cervix, and completely resected papillary thyroid and follicular thyroid cancers
* Previous allergic reactions to janus kinase (JAK) inhibitors or excipients
* Prior therapy with ruxolitinib or other JAK inhibitors
* Subjects who have had major surgery within 4 weeks prior to entering the study
* Subjects who are anticipated to receive a transplant within the first 6 months of treatment on trial