It is the most common of a group of tumours known as soft tissue sarcomas. These develop from muscle or fibrous tissue and can affect many different parts of the body.
The most common areas of the body to be affected are around the head and neck, the bladder or the testes. Sometimes the tumours are found in muscles of the limbs and in the chest or abdominal wall. Occasionally if the tumour is in the head or neck region, it can spread into the brain or spinal fluid.