Sarcomas are cancers that begin in the body's connective tissues.

They are often divided into two groups. One group is bone cancer, which begins in the hard part of the bone. The other group is soft tissue sarcomas, which start in muscles, fat, fibrous tissue, blood vessels, nerves, or other supportive tissues of the body.

Some of these rare sarcomas include fibrosarcoma, liposarcoma, leiomyosarcoma, synovial sarcoma, hemangiosarcoma and undifferentiated sarcoma.

Undifferentiated sarcoma is a very rare childhood cancer.