Axatilimab With or Without Azacitidine for the Treatment of Patients With Advanced Phase Myeloproliferative Neoplasms, Myeloproliferative Neoplasm/Myelodysplastic Syndrome Overlap or High Risk Chronic Myelomonocytic Leukemia

This study is testing a drug called axatilimab (with or without a chemotherapy drug called azacitidine) for people with certain rare blood cancers that are in an advanced or high-risk stage. These include conditions where the bone marrow produces too many abnormal blood cells, such as chronic myelomonocytic leukemia (CMML), myeloproliferative neoplasms in accelerated phase, and related overlap disorders. **You may be eligible if...** - You are 18 or older - You have been diagnosed with one of the specific blood cancers listed in this study (such as high-risk CMML, atypical chronic myelocytic leukemia, or myeloproliferative neoplasm in accelerated phase) - Your disease has come back or not responded to prior treatment (Phase 1b), or you are newly diagnosed (Phase 2) - You are not a good candidate for intensive chemotherapy due to age or other health conditions - Your liver, kidney, and overall health function meets the study requirements **You may NOT be eligible if...** - You have already had extensive chemotherapy, azacitidine, or decitabine (more than 2 cycles of certain treatments disqualify you) - You have been diagnosed with acute myeloid leukemia (AML) - You have had an organ transplant or stem cell transplant - You have a history of pancreatitis or myositis - You are pregnant or unwilling to use contraception Talk to your doctor to see if this trial is right for you.