If you are enrolled in Phase 1, the dose of ruxolitinib you receive will depend on when you join this study. The first group of participants will receive the lowest dose level of ruxolitinib. If no intolerable side effects are seen, a second group of participants will receive a higher dose of ruxolitinib. If intolerable side effects are seen in the first group, up to 2 more groups will be enrolled and will receive lower doses than the first group.