Squamous cell carcinoma arising in dedifferentiated chondrosarcoma proved by isocitrate dehydrogenase mutation analysis.

Dedifferentiated chondrosarcoma is a primary bone tumor characterized by the presence of both low-grade cartilaginous and high-grade malignant noncartilaginous components. The high-grade noncartilaginous component is typically a pleomorphic fibroblastic spindle cell sarcoma. Dedifferentiation into a malignant epithelial component is extremely rare. In this report, we present a 74-year-old woman who developed a metastatic squamous cell carcinoma in the right inguinal area 1 year after wide resection of her right proximal femur for a dedifferentiated chondrosarcoma. The dedifferentiated component was composed of poorly differentiated epithelioid cells with foci of squamous cell carcinoma. Mutational analysis was performed, and the isocitrate dehydrogenase 1 R132C mutation was detected in the low-grade chondrosarcoma, dedifferentiated chondrosarcoma as well as the metastatic squamous cell carcinoma. And this mutation was not detected in patient's normal tissue. Our study supports the theory that both the chondrosarcoma cells and dedifferentiated epithelioid tumor cells arose from the same clonal origin.