3. Pregnancy or breastfeeding. Women (patients or partners of male patients) of childbearing potential (WOCBP) must practice acceptable methods of birth control to prevent pregnancy. All WOCBP MUST have a negative pregnancy test within 4 weeks prior to registration, and this must be repeated within 72 hours prior to first receiving ruxolitinib. If the pregnancy test is positive, the patient must not receive ruxolitinib and must not be enrolled in the study.