Definition: A type of disease in which the bone marrow makes too many red blood cells, platelets, or certain white blood cells. Myeloproliferative neoplasms usually get worse over time as the number of extra cells build up in the blood and/or bone marrow. This may cause bleeding problems, anemia, infection, fatigue, or other signs and symptoms. Certain myeloproliferative neoplasms may become acute myeloid leukemia (AML). Myeloproliferative neoplasms include chronic myelogenous leukemia (CML), polycythemia vera, primary myelofibrosis, essential thrombocythemia, chronic neutrophilic leukemia, and chronic eosinophilic leukemia.