Myelofibrosis is an uncommon type of bone marrow cancer that disrupts body's normal production of blood cells.

Myelofibrosis causes extensive scarring in bone marrow, leading to severe anemia that can cause weakness and fatigue. It can also cause a low number of blood-clotting cells called platelets, which increases the risk of bleeding. Myelofibrosis often causes an enlarged spleen.

Myelofibrosis is considered to be a chronic leukemia — a cancer that affects the blood-forming tissues in the body. Myelofibrosis belongs to a group of diseases called myeloproliferative disorders.

Some people with myelofibrosis have no symptoms and might not need treatment right away. Others with more-serious forms of the disease might need aggressive treatments right away. Treatment for myelofibrosis, which focuses on relieving symptoms, can involve a variety of options.

SYMPTOMS OF MYELOFIBROSIS

• Feeling tired, weak or short of breath, usually because of anemia
• Pain or fullness below your ribs on the left side, due to an enlarged spleen
• Easy bruising
• Easy bleeding
• Excessive sweating during sleep (night sweats)
• Fever
• Bone pain

CAUSES OF MYELOFIBROSIS

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  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 with varying levels of platelets. In people with myelofibrosis, the normally spongy bone marrow becomes scarred.

RISK FACTORS

Although the cause of myelofibrosis often isn't known, certain factors are known to increase your risk:

• Age. Myelofibrosis can affect anyone, but it's most often diagnosed in people older than 50.
• Another blood cell disorder. A small portion of people with myelofibrosis develop the condition as a complication of essential thrombocythemia or polycythemia vera.
• Exposure to certain chemicals. Myelofibrosis has been linked to exposure to industrial chemicals such as toluene and benzene.
• Exposure to radiation. People exposed to very high levels of radiation have an increased risk of myelofibrosis.

COMPLICATIONS

Complications that may result from myelofibrosis include:

• Increased pressure on blood flowing into liver. Normally, blood flow from the spleen enters in liver through a large blood vessel called the portal vein. Increased blood flow from an enlarged spleen can lead to high blood pressure in the portal vein (portal hypertension). This in turn can force excess blood into smaller veins in your stomach and esophagus, potentially causing these veins to rupture and bleed.
• Pain. A severely enlarged spleen can cause abdominal pain and back pain.
• Growths in other areas of body. Formation of blood cells outside the bone marrow (extramedullary hematopoiesis) may create clumps (tumors) of developing blood cells in other areas of  body. These tumors may cause problems such as bleeding in gastrointestinal system, coughing or spitting up of blood, compression of your spinal cord, or seizures.
• Bleeding complications. As the disease progresses, your platelet count tends to drop below normal (thrombocytopenia) and platelet function becomes impaired. An insufficient number of platelets can lead to easy bleeding — an issue that you and your doctor will want to discuss if  contemplating any type of surgical procedure.
• Acute leukemia. Some people with myelofibrosis eventually develop acute myelogenous leukemia, a type of blood and bone marrow cancer that progresses rapidly.