Answer: Myxoid chrondrosarcoma

Histology: Myxoid chondrosarcoma is a multinodular tumor of the extremities in older adults composed of cords of relatively small polygonal cells with scanty cytoplasm in a hemorrhagic myxoid stroma. Note that the tumor has few vessels and lacks the rich vascular pattern that typifies myxoid liposarcoma though the uniform round cells appear similar. The tumor occurs both in bone and, more commonly in soft tissue, but the specific t(9;22)(q21-31;q12.2) rearrangement is found only in examples arising in extraskeletal locations (Brody). This finding may occasionally be exploited to identify cellular and pleomorphic variants of myxoid chondrosarcoma. The survival curve is unusual in myxoid chondrosarcoma in that, although many succumb, patients can survive for many years with metastatic disease. For example, of 31 patients with follow-up in an earlier study by Enzinger and Shiraki, 4 patients had died of disease and 3 living patients were alive with metastatic disease at 6, 10, and 6 years after the onset of metastases, respectively. A more recent large study by Meis-Kindblom (1999) and others confirmed a protracted survival curve in myxoid chondrosarcoma with estimated survival at 5, 10, and 15 years at 90%, 70%, and 60%, respectively. These authors found no correlation between tumor grade and prognosis.

Discussion: As above, myxoid chondrosarcoma differs from myxoid liposarcoma by the lack of delicate “chickenwire” vasculature in the former. Lipoblasts, which tend to be more frequent around vessels and at the periphery of lobules, are lacking in myxoid chondrosarcoma. Both lesions may express S100 protein. Myxomas show little vascularity and their constituent cells are more stellate than round. They are S100 negative. Myxofibrosarcomas are richly vascularized with curvilinear vessels which appear similar to the vessels in myxoid liposarcomas but the proliferating cells in these are also stellate and display atypia.