Myelofibrosis is a rare type of blood cancer that affects the bone marrow, leading to the formation of fibrous scar tissue inside the bone marrow. This scar tissue impairs the bone marrows ability to produce normal blood cells, leading to a variety of symptoms and complications. Myelofibrosis can occur on its own (primary myelofibrosis) or develop from another bone marrow disorder (secondary myelofibrosis). Some people with myelofibrosis have no symptoms and might not need treatment right away, while others with more serious forms of the disease might need aggressive treatments right away. Symptoms of myelofibrosis include fatigue, weakness, shortness of breath, pale skin, frequent infections, and an enlarged spleen. Treatment for myelofibrosis focuses on relieving symptoms and can involve a variety of options, including stem cell or bone marrow transplants.