Introduction

In myeloproliferative disorders (myelo = bone marrow, proliferative = rapid multiplication), the blood-producing cells in the bone marrow (precursor cells) develop and reproduce abnormally or are crowded out by an overgrowth of fibrous tissue.

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

See the table Major Myeloproliferative Disorders.