Extraskeletal cutaneous chondroblastic osteosarcoma: a case report.

Extraskeletal osteosarcoma is an uncommon neoplasm that usually arises in the deep soft tissues, especially in the lower extremities, with rare cases involving the subcutis or dermis. We report a 60-year-old man with an enlarging cutaneous mass in the right lower thigh. An incisional skin biopsy showed a well-defined, but non-encapsulated neoplasm, characterized by extensive cartilage with marked cellularity, atypia and high mitotic activity, involving the dermis and subcutis. Although osteoid or bone was not observed, a diagnosis of cutaneous chondroblastic osteosarcoma was suggested after excluding an origin in bone or other primary tumor sites by imaging techniques. Histopathologic features of the surgical specimen were characteristic, with a predominant high-grade chondroid component together with focal fibrosarcomatous zones, areas of multinucleated giant cells and foci of bone and osteoid formation. The patient underwent postoperative chemotherapy and is currently alive with pulmonary metastases 15 months after surgery. In summary, we report a unique case of cutaneous osteosarcoma of the chondroblastic subtype, diagnosed on incisional skin biopsy despite the absence of osteoid or bone during tumor sampling. As a rule, when an obviously malignant 'chondrosarcoma' is identified, one should always consider this entity.