Primary myelofibrosis is a disorder of the bone marrow, in which the marrow is replaced by fibrous (scar) tissue.
In primary myelofibrosis, a progressive scarring (fibrosis) of the bone marrow occurs. As a result, blood forms in sites other than the bone marrow, such as the liver and spleen. This causes an enlargement of these organs. The cause and risk factors are unknown.
The disorder usually develops slowly, in people over 50 years old. It leads to progressive bone marrow failure with severe anemia. Low platelet count leads to easy bleeding, and spleen enlargement continues.
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