Primary extraskeletal mesenchymal chondrosarcoma in fossa poplitea of a 93-year-old woman.

We report the case of a 93-year-old female who had developed a primary extraskeletal chondrosarcoma in Fossa poplitea for many years. This rare, highly malignant tumor occurred in unusual location and at unusual age. Histologically, it presented with sheets of primitive mesenchymal cells and islets of well-differentiated cartilaginous tissue. Immunohistochemical preparations revealed a positivity for neuron-specific enolase and vimentin, the cartilaginous portion of the tumor and isolated cells of the undifferentiated area also stained partially for S-100 protein. Three years later, only one metastasis was found in the contralateral lower extremity.