Myeloproliferative neoplasms (MPNs) are cancers of the blood and bone marrow. They start when something goes awry with hematopoietic stem cells—immature cells that can develop into any type of blood cell. Myeloid cells, also found in the bone marrow, can develop abnormalities as well. As cancerous cells tend to do, the affected blood cells proliferate, crowding out normal cells. ...
