In myeloproliferative disorders (myelo = bone marrow, proliferative = rapid multiplication), the blood-producing cells in the bone marrow (precursor cells) develop and reproduce excessively or are crowded out by an overgrowth of fibrous tissue. Typically, these disorders are acquired and not inherited, although rarely there are families in which several members have these disorders. It is likely that family members inherit a predisposition to the disorder rather than the disorder itself.

Three major myeloproliferative disorders are polycythemia vera, myelofibrosis, and thrombocythemia. The proliferation of blood-producing cells is always noncancerous (benign) when it begins. However, in a small number of people, a myeloproliferative disorder progresses or transforms to a cancerous (malignant) condition, such as leukemia.

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Major Myeloproliferative Disorders Disorder Bone Marrow Characteristics Blood Characteristics Polycythemia vera Increased number of cells that produce the circulating blood cells Increased number of red blood cells Often, increased number of platelets and white blood cells Myelofibrosis Excess fibrous tissue Increased number of immature red and white blood cells Misshapen red blood cells Decreased overall number of red blood cells (anemia) The numbers of white blood cells and platelets often eventually decrease, but in some people they increase Thrombocythemia Increased number of cells that produce platelets (megakaryocytes) Increased number of platelets

Last full review/revision July 2008 by Josef T. Prchal, MD