Extraskeletal myxoid chondrosarcoma: a Multi-Institutional Study of 42 Cases in Japan.

Background: Extraskeletal myxoid chondrosarcoma (EMC) is a rare malignant neoplasm. Despite a consensus for the distinct clinicopathologic entity of EMC, its clinical features remain controversial. In addition, most studies have contained a small number of patients who underwent definitive surgical treatment.

Methods: Forty-two cases of EMC, which had been identified from files of eight affiliated hospitals and confirmed for histologic diagnosis at the Pathology Center, were analyzed for histologic grade, demographics, treatments, outcomes, and prognostic factors. The average follow-up period was 7.4 years.

Results: Included in the study were 20 men and 22 women with a mean age at diagnosis of 52.1 years. The tumors were located mainly in the lower extremities (69%). Thirty-three tumors (79%) were classified as Grade 1 and nine as Grade 2 according to the modified French System. Overall survival was 100% at 5 years and 88% at 10 years. Disease-free survival was 45% at 5 years and 36% at 10 years. Inadequate initial surgery was defined as a significant risk factor for local recurrence by univariate analysis of all 42 patients but not by the analysis of those 30 patients who had undergone wide tumor excision or amputation. Wide excision led to the recurrence rate of 14%.

Conclusions: These findings supported the role of wide excision in the local control of EMC, irrespective of the previous excision procedure or recurrence. The protracted clinical course of the tumors and the presence of patients who had distant metastasis develop after definitive surgery of the primary tumor represented EMC as intermediate malignancy.