Myeloproliferative neoplasms (MPN) are cancers that start in the bone marrow, where blood cells are made. In MPN, the bone marrow makes too many of one or more types of blood cells (red blood cells, white blood cells and/or platelets). These cells change the thickness of the blood. Sometimes they don’t work properly. They also crowd the bone marrow and then it can’t make enough healthy blood cells.
