Cancer in the bone marrow means the cancer cells have made their way into the bone marrow. This is supposedly very painful. When cancer is in the marrow, it spreads more quickly throughout the body. The prognosis for this bone cancer type isn't very good. Leukemia is a well known bone marrow cancer. Bone marrow cancer is pretty rare and it only accounts for less than 1% of all new cancer diagnosed. The symptoms are pain in the bones and joints, swelling of the bones and joints and many unexplained infections. Other less common symptoms are unexplained weight loss, fever and severe sweating. This type of cancer is more common in males.