A Study of Ruxolitinib in Combination With Abemaciclib for the Treatment of Myelofibrosis

This study is testing whether combining two medications — ruxolitinib (already used to treat myelofibrosis) and abemaciclib (a cancer drug that targets cell growth) — works better than ruxolitinib alone for people with myelofibrosis who are not responding adequately to ruxolitinib. Myelofibrosis is a bone marrow cancer that causes scarring, an enlarged spleen, fatigue, and other debilitating symptoms. You may be eligible if: - You have myelofibrosis (primary or secondary after polycythemia vera or essential thrombocythemia) classified as intermediate or high risk - You have been on ruxolitinib for at least 12 weeks at a stable dose of 10 mg or 15 mg twice daily - You still have an enlarged spleen (5 cm or more below the left rib margin) and/or significant symptoms despite ruxolitinib treatment - You are 18 or older with adequate organ function - You are able to use effective contraception if you can become pregnant or father a child You may NOT be eligible if: - You have previously been treated with a CDK4/6 inhibitor - You have been in another experimental treatment trial in the past 30 days - You have active brain involvement from the cancer (CNS leukemia) - You have an active serious infection (bacterial, fungal, or HIV/hepatitis B or C) - You are pregnant or breastfeeding - You have serious heart conditions including a history of ventricular arrhythmia, sudden cardiac arrest, or syncope from a heart cause - You cannot swallow pills or have a serious gastrointestinal condition Talk to your doctor to see if this trial is right for you.