NCI: A rare, aggressive cancer that usually affects young males and usually is located in the abdomen.,MSH: A rare, aggressive soft tissue sarcoma that primarily affects adolescents and young adults. It is most commonly found in the abdomen.,NCI: A tumor composed of small round tumor cells of uncertain histogenesis, associated with prominent stromal desmoplasia and polyphenotypic differentiation. There is a recurrent cytogenetic aberration: t(11;22)(p13;q12).,NCI: An aggressive malignant neoplasm of uncertain lineage. It is characterized by the presence of small round cells in a desmoplastic stroma. It usually affects children and young adults. The most common site of involvement is the abdomen. Patients usually present with abdominal distention, pain, ascites, and a palpable abdominal mass. The prognosis is usually poor.