Low-grade fibromyxoid sarcoma of the small intestine: report of 4 cases with molecular cytogenetic confirmation.

Low-grade fibromyxoid sarcoma (LGFMS) is a rare soft tissue tumor that typically involves the deep soft tissues of the extremities. However, LGFMS has been described in other locations including the head and neck, retroperitoneum, and mesentery. Translocations involving the FUS gene located at 16p are considered to be highly specific for the diagnosis of this tumor when present in conjunction with the appropriate morphologic appearance. We report 4 cases of LGFMS arising in the small bowel. The patients' ages (3 female, 1 male) ranged from 52 to 71 years (median, 61 y). None of the patients had a history of soft tissue sarcoma. An intramural tumor was presented in all cases, ranging from 4.5 to 14.5 cm in greatest diameter (mean, 10 cm). Microscopically, the tumors consisted of an admixture of hypocellular, heavily collagenized zones and more cellular myxoid nodules, containing a greater number of neoplastic cells arranged around characteristic curvilinear vessels. By immunohistochemistry, all tumors were positive for vimentin and negative for smooth muscle actin, CD117, CD34, and S100 protein. Fluorescence in situ hybridization for rearrangement of the FUS locus at 16p11 was positive in 3 informative cases. Follow-up information was available in 3 cases; 2 patients are alive without disease and another patient died of disease. We conclude that LGFMS should be included in the differential diagnosis of fibrous or myxoid spindle cell tumors of the gastrointestinal tract. On the basis of limited follow-up, the natural history of enteric LGFMS seems to be similar to that of LGFMS in other locations, with potential for late metastases.