Primary bone carcinosarcoma: chondrosarcoma and squamous cell carcinoma with keratin pearl formation.

Malignant bone tumors with epithelial differentiation are extremely rare. Only one case of primary malignant bone tumor with distinct squamous cell carcinoma and chondrosarcoma has ever been reported. Reported herein is a case of primary malignant bone tumor with distinct squamous cell carcinoma and chondrosarcoma, so-called carcinosarcoma of bone, arising in the femur of a 53-year-old man. The tumor was located within the femur and was diagnosed by curettage as a well-differentiated chondrosarcoma. No primary tumor was detected in any other organ. Within a few months the tumor had rapidly grown toward the soft tissue, and hemipelvectomy was performed. Examination of the surgical specimen revealed that the tumor was mainly composed of undifferentiated spindle sarcoma cells with scattered foci of chondrosarcoma and of squamous cell carcinoma with keratin pearl formation. The patient died approximately 6 months postoperatively. At autopsy multiple metastases were detected in the heart, both lungs, muscles, and lymph nodes. Interestingly, the chondrosarcoma and squamous cell carcinoma components were observed in several metastatic foci. The tumors in both the previously reported case and the present case contained components of chondrosarcoma and squamous cell carcinoma with keratin pearl formation, and this combination of histological features may be a unique characteristic of carcinosarcoma of bone.