Gliosarcoma Arising in Oligodendroglial Tumors (“Oligosarcoma”)

Gliosarcomas are morphologically biphasic tumors composed of glial and sarcomatous elements. Only rare examples of gliosarcoma with oligodendroglial components have been reported. Seven patients with oligodendroglial tumors and a sarcomatous component were identified. Fluorescence in situ hybridization for 1p/19q was sought in glial and sarcomatous regions in all cases. Their mean age at diagnosis of gliosarcoma was 48 years (range 36 to 68) (F:M ratio=5:2). At first resection, the tumors included grade II oligodendroglioma (n=3), grade III oligodendroglioma (n=1), grade II oligoastrocytoma (n=1), and grade III oligoastrocytoma (n=2). The sarcomatous component developed in recurrent/progressive tumors in 6 cases but was a focal finding at first tumor resection in 1 and included fibrosarcoma (n=5), leiomyosarcoma (n=1), or pleomorphic myogenic sarcoma (n=1). Rhabdoid change was a focal finding in the sarcomatous component of 1 tumor. The glial component expressed both glial fibrillary acidic protein and S-100 in all cases, whereas the sarcomatous component at least focally showed smooth muscle actin (n=6), CD34 (n=4), S-100 protein (n=3), and epithelial membrane antigen (n=2) reactivity. Fluorescence in situ hybridization studies demonstrated 1p/19q codeletion in 5 cases, showed no evidence of deletion in 1 case, and technically failed in 1 case. Three of the 5 cases demonstrated 1p/19q codeletion in the sarcomatous component as well. Gliosarcomas with oligodendroglial elements are rare. The relatively frequent presence of 1p/19q codeletion in both glial and sarcomatous components supports the notion that the sarcomatous component represents a metaplastic change occurring in the glial element, the same mechanism active in classic astrocytic gliosarcomas.