Extra-axial chordoma: a clinicopathologic analysis of six cases.

Extra-axial chordoma is an exceedingly rare tumor, with only 28 cases reported in the literature to date. Axial and extra-axial chordoma exhibits complete morphologic and immunophenotypic (expression of brachyury) overlap. However, in consideration of the non-canonical presentation, extra-axial chordoma is under-recognized and often misdiagnosed, most often as extraskeletal myxoid chondrosarcoma or myoepithelioma. To increase our understanding of the clinicopathologic features of extra-axial chordoma, six cases have been retrieved from the files of the Istituto Ortopedico Rizzoli and of the General Hospital of Treviso. The clinicoradiologic, morphologic, and molecular features have been analyzed, and the follow-up was updated. Our series included four female and two male patients; their ages ranged from 20 to 67 years (mean 45.8 years). All patients presented with a single mass localized in four cases in the soft tissue (posterior arm, left leg, dorsal aspect of the foot, and popliteal fossa), and in two cases in the bone (radius and second metacarpal bone). Grossly, the neoplasm was lobulated, with a fleshy cut surface and a diameter ranging between 0.8 and 8 cm (mean 3.4 cm). Morphologically, all six cases showed an epithelioid cell proliferation organized in nests and cords demarcated by fibrous septa and set in an abundant extracellular myxoid matrix. Neoplastic cells featured hyperchromatic nuclei and abundant vacuolated cytoplasm. Immunohistochemically, all six cases were strongly positive for EMA, cytokeratin AE1/AE3, S100, and brachyury. INI1 nuclear expression was retained. Smooth muscle actin, calponin, p63, and GFAP were all negative. Fluorescent in situ hybridization (FISH) analysis did not reveal rearrangements involving NR4A3, FUS, and EWSR1 genes. At follow-up (mean 55 months), all patients were alive without disease after local surgical treatment. One patient underwent thigh amputation following multiple local recurrences and inguinal node metastases treated with marginal resection. In conclusion, primary extra-axial chordoma is an extremely rare neoplasm with distinct morphological and immunohistochemical features. Immunomorphology and molecular analysis allow distinction from both extraskeletal myxoid chondrosarcoma and myoepithelioma. Complete surgical resection appears to be curative.