Primary myelofibrosis (PMF) is also called chronic idiopathic myelofibrosis or myelofibrosis with myeloid metaplasia. This condition is caused by an overproduction of cytokines due to reactive processes, which results in the formation of abnormal hematopoietic progenitor cell clones. The condition is also associated with a marked buildup of fibrotic tissue in the bone marrow, which further hinders the production of normal, healthy cells. Consequently, extramedullary hematopoeisis begins as the bone marrow cannot function adequately. The fibroblasts themselves are not part of the clonal neoplasm, but their over-production is a secondary phenomenon. The image on the right demonstrates an overgrowth of fibrous tissue in the bone marrow, an important diagnostic feature of primary myelofibrosis.
PMF predominantly affects individuals over age 60. The median survival is approximately 3-5 years. Patients diagnosed at an earlier age have a median survival of 11 years.