**Pacritinib vs. Hydroxyurea in Advanced Proliferative Chronic Myelomonocytic Leukemia** This study is for adults with advanced proliferative chronic myelomonocytic leukemia (CMML), a type of blood cancer. Researchers want to see if the drug pacritinib works better than hydroxyurea. Pacritinib and hydroxyurea are medicines that help control blood cell growth. Participants will get either pacritinib or hydroxyurea for about 48 weeks. After that, they'll be checked on for another year. **Key Points:** - **Time Commitment:** The study lasts up to 48 weeks, plus follow-ups for a year. - **Treatment Plan:** You'll take either pacritinib or hydroxyurea. If one isn't working by week 24, you might switch to pacritinib. - **Safety Monitoring:** An independent group will ensure the study is safe, checking in every 6 months. **Eligibility:** You can join if you have CMML-1 with specific blood counts and no other recent major health issues. Women must test negative for pregnancy and use contraception. You cannot join if you had certain cancers recently or other treatments conflicting with the study drugs.