RESUMO
Primary cutaneous osteosarcoma is an exceedingly rare malignant mesenchymal neoplasm of the skin which produces bone, osteoid, or chondroid material and does not involve the underlying bone. The most common site for extraskeletal osteosarcoma is in the deep soft tissues of the thigh, upper extremities, and retroperitoneum; however, it may occur anywhere in the body. Involvement of the skin is rare and when it does occur it is more commonly due to metastatic disease rather than a primary malignancy. Only 16 cases of primary cutaneous osteosarcoma have been described in the literature. We report an uncommon case of primary cutaneous osteosarcoma. Our patient is an 84-year-old male with an unremarkable medical history who presented to the dermatology clinic complaining of a 0.5 x 0.4 cm pink flesh to translucent-appearing, shiny, papule on the right superior jawline which was not connected to the underlying bone. Clinically the differential diagnosis included basal cell carcinoma, trichoepithelioma, and other cutaneous adnexal tumors. An excisional biopsy was performed which demonstrated an unremarkable epidermis with a hypercellular reticular dermis with occasional large spindled cells with amphophilic cytoplasm. The deep dermis was involved by mature osteoid formation and infiltration of highly mitotically active, atypical epithelioid and spindled cells with abundant nuclear pleomorphism, amphophilic cytoplasm, and poorly defined cell borders. Occasional multinucleate forms were seen. Immunohistochemistry was performed which showed strong positive staining with vimentin. Without connection to the underlying bone, osteosarcoma of periosteal, parosteal, or osseous origin was excluded. Based on these histomorphologic findings, a diagnosis of primary cutaneous osteosarcoma was made. Our case adds to the dearth of literature regarding primary cutaneous osteosarcoma and provides primary care physicians, dermatologists, and pathologists much needed insight into this rare condition.