Sarcoma is a rare cancer of the soft tissues and bone. Most types of cancer originate in the epithelial linings that cover exposed surfaces of the body and have direct exposure to environmental toxins. Sarcomas, however, originate from cells or tissues that lie below these linings in the muscle, bone, cartilage, fat, blood vessels, smooth muscle and skeletal muscles. Any type of tissue in the body can give rise to a sarcoma.