Myeloproliferative neoplasms and myelodysplastic syndromes are diseases of the blood cells. They include chronic myeloproliferative neoplasms, myelodysplastic syndromes, and myelodysplastic/myeloproliferative neoplasms.

Chronic myeloproliferative neoplasms are diseases in which the bone marrow makes too many red blood cells, platelets, or certain white blood cells.

Myelodysplastic syndromes are a group of cancers in which immature blood cells in the bone marrow do not mature or become healthy blood cells.

Myelodysplastic/myeloproliferative neoplasms are diseases that have features of both myelodysplastic syndromes and myeloproliferative neoplasms.

Certain types of myeloproliferative neoplasms and myelodysplastic syndromes may become a type of blood cancer called acute leukemia.