A sarcoma is a type of cancer that develops from certain tissues, like bone or muscle. There are 2 main types of sarcoma: bone sarcomas and soft tissue sarcomas. Soft tissue sarcomas - can develop from soft tissues like fat, muscle, nerves, fibrous tissues, blood vessels, or deep skin tissues. They can be found in any part of the body. Most of them develop in the arms or legs. They can also be found in the trunk, head and neck area, internal organs, and the area in back of the abdominal cavity (known as the retroperitoneum). Sarcomas are not common tumors, and most cancers are the type of tumors called carcinomas. There are many types of soft tissue tumors, and not all of them are cancerous. When a tumor is not cancerous, it is called benign. When the term sarcoma is part of the name of a disease, it means the tumor is malignant (cancer). There are about 50 different types of soft tissue sarcomas. Learn more about Soft Tissue Sarcoma Sarcomas occurring in bone, such as Osteosarcoma and malignant fibrous histiocytoma (MFH) of the bone are diseases in which malignant (cancer) cells form in bone. Osteosarcoma usually starts in osteoblasts, which are a type of bone cell that grows into new bone tissue. Osteosarcoma is most common in teenagers and young adults. It commonly forms in the ends of the long bones of the body, which include bones of the arms and legs. In children and teenagers, it often develops around the knee. Rarely, osteosarcoma may be found in soft tissue or organs in the chest or abdomen. Learn more about Bone Cancer