Comparing Momelotinib and Ruxolitinib in People With Untreated Myelofibrosis and Low Blood Cell Counts

This study is being done to answer this question:

Does momelotinib or ruxolitinib do a better job at shrinking the spleen in people who have myelofibrosis with low blood cell counts and haven't been treated yet?

Other goals of this study are to find out:

* Which drug does a better job of preventing the need for blood transfusions or other treatments * Which drug does a better job of reducing myelofibrosis symptoms * What side effects the drugs cause

Momelotinib and ruxolitinib are JAK inhibitors. JAK inhibitors are medicines that block a type of protein that can cause the immune system to be too active, which can cause pain and swelling (including in the spleen). JAK inhibitors are the most commonly used drugs for myelofibrosis that has caused serious symptoms including swelling in the spleen.

There are many different JAK inhibitors approved by the FDA to treat myelofibrosis, but no previous studies have compared these drugs with each other for treating myelofibrosis in people with low blood cell counts who haven't been treated yet.