OBJECTIVETo study the clinicopathologic features, diagnosis and differential diagnosis of extraskeletal myxoid chondrosarcoma (EMC).

METHODSThe clinical and pathologic features of 7 cases of EMC encountered in Fujian Provincal Hospital and Fuzhou General Hospital of Nanjing Military Command during the period of 2005 to 2015 were analyzed. Immunohistochemical study and PAS staining were carried out. Relevant literature was reviewed.

RESULTSThe male-to-female ratio was 6 to 1. The age of patients ranged from 21 to 50 years (median = 36 years). The maximum tumor dimension ranged from 2.5 to 15.0 cm (mean = 8.4 cm). The sites of involvement included left neck, right shoulder, left thigh, right thigh, right upper arm and abdomen. Most patients presented with painless lumps. Histologically, all cases showed similar features. Low-power examination showed a nodular or lobulated architecture, with intervening fibrous septa and myxoid matrix in the background. The tumor cells were arranged in cords or tufted clusters. They were spindly to epithelioid / rhabdoid (plasmacytoid) in shape, with eosinophilic to sometimes vacuolated cytoplasm. Intracytoplasmic eosinophilic inclusion bodies and coagulative necrosis were focally seen. Mitotic figures were rare (less than 2 per 10 high-power fields). Immunohistochemical study showed that the tumor cells were positive for vimentin (7/7) and INI1 (7/7). They were focally positive for CKpan (2/7), p63 (3/7), CD99 (3/7), S-100 protein (1/7) and synaptophysin (2/7). Ki-67 proliferation index ranged from 10% to 40%. The tumor cells were negative for α-smooth muscle actin, desmin, myoD1, CD34 and CD117. The cytoplasm of the tumor cells was positive for PAS. EWSR1 gene signal was detected in 5 cases.

CONCLUSIONSEMC is a rare malignant mesenchymal tumor. Arrival at correct diagnosis relies on morphologic examination and immunohistochemistry. Molecular pathology is helpful when necessary. The primary treatment modality for EMC is complete surgical excision and the prognosis is satisfactory.