A soft-tissue sarcoma (STS) is a malignant tumour, a type of cancer, that develops in soft tissue. A soft tissue sarcoma is often a painless mass that grows slowly over months or years. They may be superficial or deep-seated. Any such unexplained mass will need to be diagnosed by biopsy. Treatment may include, surgery, radiotherapy, chemotherapy, and targeted drug therapy. The other type of sarcoma is a bone sarcoma.
There are many types. The World Health Organization lists more than fifty subtypes.