| Disease | Malignant mesenchymal neoplasm of uncertain differentiation. |
| Epidemiology | Extraskeletal myxoid chondrosarcoma is a rare tumor, encompassing 2.3% of soft tissue sarcomas in a Japanese series. Mean ages reported in various series range from 46 to 57 years. Males are affected about twice as often as females. |
| Clinics | Location: deep soft tissues of the lower extremities in about 75% of the cases, especially the thigh, the popliteal fossa, and the buttock, and can also occur in the trunk, abdomen, and head and neck. |
| Pathology | Macroscopic findings: the tumor presents as lobulated or multinodular mass, generally well circumscribed with pseudocapsule. The size of the tumor at the time of diagnosis may vary from 1 to about 20 cm (median size 7 cm). Histology: Lobulated architecture with uniform round to spindled cells forming interconnecting cords, clusters, or trabeculae in a background of myxoid matrix. The tumor cells have variably eosinophilic or vacuolated cytoplasm that extends to form the reticular growth pattern. A subset of tumors shows hypercellularity, higher grade cytomorphology, and epithelioid or rhabdoid features. A subset of tumors is positive for S100, CD117, synaptophysin, and neuron-specific enolase. INI1 loss is observed in a subset, often with rhabdoid features. Ultrastructurally, at least one third of the tumors demonstrate microtubular aggregates within dilated rough endoplasmic reticulum. |
| Treatment | Treatment: surgical excision, with possible adjuvant chemotherapy. |
| Prognosis | Prognosis: high rates of local and distant recurrence, including pulmonary metastasis, but with associated prolonged survival. |
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