SKELETAL AND EXTRASKELETAL MYXOID CHONDROSARCOMA - A COMPARATIVE CLINICOPATHOLOGICAL, ULTRASTRUCTURAL, AND MOLECULAR STUDY

BACKGROUND, Skeletal myxoid chondrosarcoma (SMC) is considered to be e ither a typical chondrosarcoma with prominent myxoid alterations or an altogether unique malignant cartilage tumor. Extraskeletal myxoid cho ndrosarcoma (EMC) is a relatively rare but well-recognized neoplasm. I t was initially thought to be a low grade sarcoma of cartilage derivat ion and was recently found, in most cases, to contain a reciprocal t(9 ;22), resulting in a fusion of the EWS and CHN genes. Are SMC and EMC the same entity arising in two different locations, or are they two se parate entities? To the authors' knowledge, this study represents the first systematic attempt to answer this question. METHODS. Forty conse cutive cases of EMC (20 cases) and SMC (20 cases) were compared by lig ht and electron microscopy, immunohistochemistry, and molecular analys is. The mean clinical follow-up for both groups was 55 months. Histolo gic criteria for SMC consisted of 95% myxoid matrix, with only minimal hyaline cartilage formation. RESULTS. The gender distribution was ide ntical in both groups (13 males and 7 females). The mean age was 55 ye ars for EMC patients and 45 years for SMC patients. The EMC tumors wer e predominantly located in the deep soft tissues of the lower extremit y (60%) and buttock (20%), and the mean tumor size was 13 cm. SMC was most commonly located in the bones around the hip joint (pelvis 35%; p roximal femur 20%) and shoulder (20%); the mean size was 9 cm. Histolo gic grade in the EMC group correlated with survival (82% of the high g rade tumors metastasized). Electron microscopy performed in 8 EMC case s revealed intracisternal microtubules in 3 cases and prominent mitoch ondria in 5, whereas in 5 SMC cases it revealed only inconspicuous org anelles. Molecular analysis for the EWS-CHN fusion RNA resulting from the t(9;22) was performed in 15 cases (9 EMC and 6 SMC) and was detect ed in 7 of 9 EMC cases and 0 of 6 SMC cases. In one case, the molecula r structure of the EWS-CHN fusion RNA was novel. The probability of me tastasis was significantly higher (P = 0.004) for the EMC group than f or the SMC group. CONCLUSIONS. Although similar light microscopic feat ures are noted in EMC and SMC, fundamental differences are noted at th e ultrastructural and molecular levels, suggesting that EMC and SMC re present two distinct entities in the chondrosarcoma family of tumors. Cancer 1998;83:1504-21. (C) 1998 American Cancer Society.