Primary cutaneous extraskeletal osteosarcoma of the pretibial leg: A case report and summary of the literature.

Primary cutaneous extraskeletal osteosarcoma is a rare tumor, with fewer than 30 known cases worldwide. We report the case of a 60-year-old female who presented with a solitary right pretibial nodule of 3 mm. She had no known comorbidities, trauma to the area, or prior malignancy. The biopsy specimen showed abundant mineralized osteoid, in which pleomorphic and spindled cells with anaplastic features were embedded. The osteoid matrix in this case contained overtly malignant cells, with frequent mitotic figures, as well as multinucleated giant cells. Immunohistochemistry and imaging led to the conclusion that this nodule represented a primary cutaneous extraskeletal osteosarcoma. The previously reported cases are variable in location, size, gross appearance, and clinical course. The prognosis of osteosarcoma is typically poor, with aggressive behavior; this, however, may be less severe in these strictly cutaneous tumors, though additional follow-up would be beneficial to determine long-term outcomes for the known cases. Ultimately, despite the fact that this is an extremely rare entity, primary cutaneous extraskeletal osteosarcomas should be considered when relevant.