Causes

Myelofibrosis occurs when bone marrow stem cells develop changes (mutations) in their DNA. The stem cells have the ability to replicate and divide into the multiple specialized cells that make up your blood — red blood cells, white blood cells and platelets.

It's not clear what causes the genetic mutations in bone marrow stem cells.

As the mutated blood stem cells replicate and divide, they pass along the mutations to the new cells. As more and more of these mutated cells are created, they begin to have serious effects on blood production.

The end result is usually a lack of red blood cells — which causes the anemia characteristic of myelofibrosis — and an overabundance of white blood cells and varying levels of platelets. In people with myelofibrosis, the normally spongy bone marrow becomes scarred.

Several specific gene mutations have been identified in people with myelofibrosis. The most common is the Janus kinase 2 (JAK2) gene mutation. Other less common mutations include CALR and MPL. Some people with myelofibrosis don't have any identifiable gene mutations. Knowing whether these gene mutations are associated with your myelofibrosis helps determine your prognosis and your treatment.