A sarcoma can be a rare type of cancer. Sarcomas are different from the more common carcinomas, as they occur in different tissue types. Sarcomas develop in connective tissue — cells joining or helping certain tissue types in your body. These tumors are most common in your arms and legs' bones , muscles, tendons, cartilage, nerves, fat, and blood vessels but can also occur in other areas of your body. While over 50 types of sarcoma exist, they can be classified into two main categories: soft tissue sarcoma and bone sarcoma, or osteosarcoma. In 2019, roughly 12,750 cases of soft tissue sarcoma and 800-900 new cases of bone sarcoma will be diagnosed in the United States.