<p>Your soft tissues connect, support, or surround other tissues. Examples include your muscles, tendons, fat, and blood vessels. Soft tissue sarcoma is a cancer of these soft tissues. There are many kinds, based on the type of tissue they started in. They may cause a lump or swelling in the soft tissue. Sometimes they spread and can press on nerves and organs, causing problems such as pain or trouble breathing.</p> <p>No one knows exactly what causes these cancers. They are not common, but you have a higher risk if you have been exposed to certain chemicals, have had radiation therapy, or have certain genetic diseases.</p> <p>Doctors diagnose soft tissue sarcomas with a biopsy. Treatments include surgery to remove the tumor, radiation therapy, chemotherapy, or a combination.</p> <p class="">NIH: National Cancer Institute</p>