High-grade extraskeletal myxoid chondrosarcoma: a high-grade epithelioid malignancy

Aims: Extraskeletal myxoid chondrosarcoma is typically a low-to-intermediat e grade sarcoma that is associated with a prolonged clinical course, High-g rade forms are rare and not well characterized, In this series we report th e clinicopathological, immunohistochemical and ultrastructural findings in four cases of high-grade extraskeletal myxoid chondrosarcoma, Methods and results: The patients were three men and one woman (ages 34-73 years) with tumours located in the thigh (two cases), paraspinal soft tissu e and perineum. Three patients had metastases, one at 12 weeks, one at 10 m onths, and one at presentation of recurrent tumour, In the latter case the original tumour was low grade and became high grade when it recurred 3.5 ye ars later, All three patients died of disease. One patient was lost to foll ow-up. The most striking histological feature in all four tumours was the p resence of numerous large epithelioid cells. These cells were arranged in c ords within myxoid matrix and in sheets devoid of matrix. Two tumours had a reas of conventional extraskeletal myxoid chondrosarcoma intermixed with th e high-grade areas, One tumour showed transition to high-grade spindle cell sarcoma. One tumour had cells with rhabdoid features. Immunohistochemicall y, two tumours focally expressed S100 protein, and one focally expressed EM A. All were negative with cytokeratin, desmin, smooth muscle actin, HMB45, CD31 and CD34. Ultrastructural features in three cases were compatible with chondrosarcoma; one tumour had aggregates of microtubules within rough end oplasmic reticulum, a characteristic feature of this tumour. Conclusions: High-grade extraskeletal myxoid chondrosaroma is a rare and ag gressive soft tissue sarcoma, and should be included in the differential di agnosis of other epithelioid malignancies.