If you are found to be eligible to take part in this study, you will take ruxolitinib pills 2 times a day, about 12 hours apart. If you miss a dose, do not take an extra dose. Instead, take your next dose on time. If you vomit a dose within 30 minutes after taking it, you can take an extra dose to make it up for it. If you vomit and more than 30 minutes has passed since you took ruxolitinib, do not take an extra dose. Instead, take your next dose on time.