This video: Polycythemia vera (pol-e-sigh-THEE-me-uh VEER-uh) is a slow-growing type of blood cancer in which your bone marrow makes too many red blood cells. Polycythemia vera may also result in production of too many of the other types of blood cells — white blood cells and platelets. These excess cells thicken your blood and cause complications, such as such as a risk of blood clots or bleeding.
Polycythemia vera isn't common. It usually develops slowly, and you may have it for years without noticing signs or symptoms. Often, polycythemia vera is found during a blood test done for some other reason.
Without treatment, polycythemia vera can be life-threatening. However, with proper medical care, many people experience few problems related to this disease. Over time, there's a risk of progressing to more-serious blood cancers, such as myelofibrosis or acute leukemia.