Unusual giant cell-rich variant of extraskeletal osteosarcoma in the mesentery of small intestine.

Extraskeletal osteosarcoma (EOS) is an aggressive malignant soft tissue tumor, producing neoplastic osteoid without attachment to the bone or periosteum. EOS predominantly occurs in the extremities and rarely involves the abdominal cavity. Only six cases of mesenteric EOS have been reported in the English literature. We describe an unusual case of a 70-year-old female patient, who was diagnosed to have a giant cell-rich variant of mesenteric EOS arising from small bowel mesentery. This patient presented with a mesenteric mass measuring 15.1×10.3×7.5 cm. Surgical resection of the tumor with small bowel was performed. The instrumental investigations didn't reveal metastatic lesions. The patient refused further therapeutic regimen. EOS, regardless of its site or subtypes, has a very unfavorable prognosis and the patient died 2 months after discharge.