The cause of these cancers is unclear. Bone cancer can grow in any bone of the body but most do not start in the bone. Instead, they spread from other body parts such as the lung or breast. We call these metastatic bone cancers. Soft tissue cancers, like bone cancer, can also start in any part of the body. This cancer grows in fat, muscle, nerves, and blood vessels. It also grows in other soft tissues that cover or surround bone joints.