Ewing Sarcoma. Also called: Askin tumor, Ewing’s sarcoma, peripheral primitive neuroectodermal tumor, pPNET. Ewing sarcoma is a cancerous tumor that grows in the bones or in the tissue around bones (soft tissue)—often the legs, pelvis, ribs, arms or spine. Ewing sarcoma can spread to the lungs, bones and bone marrow.