A case of extraskeletal osteosarcoma with metastasis to the skin.

We present an 83-year-old woman with extraskeletal osteosarcoma (ESOS) of the breast who developed metastasis to the scalp. Skeletal osteosarcoma is the most common primary malignant neoplasm of the bone, predominantly occurring in the metaphysis of the long bones of adolescents and young adults. ESOS, in contrast, occurs primarily in the fifth and sixth decades of life, most commonly in the soft tissue of the thigh. Although the lung is overwhelmingly the most common site of metastasis for both skeletal osteosarcoma and ESOS, the skin is an uncommon metastatic site with only a few reported cases. Metastasis of ESOS to the skin is an exceedingly infrequent phenomenon, which may be a sign of widespread metastases foreboding a grim prognosis.