Extraskeletal myxoid chondrosarcoma: a reappraisal of its morphologic spectrum and prognostic factors based on 117 cases.

Extraskeletal myxoid chondrosarcoma (EMC), a phenotypically and genotypically distinctive entity, has generally been viewed as a low-grade sarcoma. No studies regarding clinical and morphologic prognostic factors have been performed on a large series of cases with long-term follow-up because of the rarity and protracted clinical course of EMC. The clinical, morphologic, and immunohistochemical features of 117 previously unreported cases were studied and statistically analyzed. The male-to-female ratio was 2:1. The median patient age was 52 years (range, 6-89 years), and the median tumor size was 7 cm (range, 1.1-25 cm). All tumors occurred within the deep subcutis or deeper soft tissues, with 80% occurring in the proximal extremities or limb girdles and 20% in the trunk. Most initial tumor excisions were intralesional or marginal. Follow-up information was available in 99 cases (median, 9 years: range, 2 months-22 years). Forty-eight patients were disease-free, and 41 patients had evidence of disease (18 of these had died of disease). Ten additional patients survived, but their disease status was unknown. There were local recurrences in 40 (48%) of 83 patients, 23 (58%) of whom had multiple local recurrences. Metastases occurred in 35 (46%) of 76 patients. The estimated 5-, 10-, and 15-year survival rates were 90%, 70%, and 60%, respectively. All cases had histologic features characteristic of classical EMC, at least focally. Cellular foci devoid of myxoid matrix and reminiscent of chondroblastoma, Ewing's sarcoma, monophasic and poorly differentiated synovial sarcoma, fibrosarcoma, and rhabdoid tumor were identified in 29% cases. Older patient age, larger tumor size, and tumor location in the proximal extremity or limb girdle were adverse prognostic factors identified by multivariate analysis. Metastasis also adversely affected survival, although local recurrence did not. This study shows that EMC has a unique clinical course, including a high rate of local recurrence, prolonged survival after metastasis in some cases, and eventually a high rate of death due to tumor. These features distinguish EMC from low-grade sarcomas. This study shows that histologic grading is of no prognostic value in EMC because prognosis is dictated primarily by certain clinical features. Histologic recognition of classical EMC and cellular and solid, nonmyxoid variants is important, however, in view of EMC's distinctive biologic behavior.