Myelofibrosis: Spontaneous scarring (fibrosis) of the bone marrow that disrupts the normal production of blood cells, leading to severe anemia and enlargement of the spleen and liver. Myelofibrosis usually begins slowly and worsens over time. It can be associated with a variety of diseases, primarily myeloproliferative (preleukemic) disorders. Also known as agnogenic myeloid metaplasia.
