Extraskeletal Myxoid Chondrosarcoma

This rare tumor occurs in all age groups but most patients are in their middle or later adult years. Males are affected twice as often as females. The tumor maypresent in the deep soft tissues of an extremity, the thigh, or the popliteal fossa. The authors have seen cases of this tumor present as small firm nodules or masses near the knee or ankle.

The tumor grows slowly and usually painlessly and is well circumscribed. It may be soft or firm.

Radiographically, a soft tissue mass is seen that lacks distinctive diagnostic features.

On pathological examination, the gross appearance of the tumor has a gelatinous, soft appearance and may appear to ba a lipoma. The surface may be gray or tan-brown, depending on the amount of hemorrhage, which is a frequent feature of this tumor.

Microscopically, there are multiple nodular features. The cells are arranged in short cords and strands or nests. Individual cells are rounded or slightly elongated and of uniform shape, with large hyperchromatic nuclei and a thin rim of eosinophilic cytoplasm.These features are characteristic of chondroblasts.

Differentiated cartilage cells are rare but may be found on careful and prolonged search. Mitotic figures are uncommon. The extracellular matrix may have a lobular, slightly basophilic or mucoid appearance.
Immunohistochemical stains show diffuse S-100 staining and strong vimentin staining. Epithelial markers are negative.

Molecular analysis of a few tumors of this type has shown a characteristic pattern marked by reciprocal translocations between chromosomes 9 and 22.

The differential diagnosis includes extraskeletal mesenchymal chondrosarcoma,myxoid liposarcoma, pleomorphic adenoma, and benign extraskeletal chondroma.

The behavior this tumor is typically slow-growing, with recurrence and late metastasis. Prognosis may be related to the cellularity, with the least cellular and most myxoid tumors having the best prognosis. Late recurrence and metastasis are common, with documented recurrence 18 years after initial excision, and pulmonary metastasis occurring 10 years after surgical removal. Other, even longer time periods have been observed. The most frequent sites of metastasis are the lung, soft tissues, and lymph nodes.

Treatment consists of complete local tumor control by resection with a wide margin. Adjunctive radiotherapy may also be helpful in reducing the chance of local recurrence.


References for this page include Enzinger and Weiss, Soft Tissue Tumors (Mosby) and Bullough and Invigorita Orthopeadic pathology.




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