Primary cutaneous osteosarcoma of the skin: a report of 2 cases with emphasis on the differential diagnoses.

Dermal or subcutaneous involvement of extraskeletal osteosarcoma is uncommon, and primary cutaneous osteosarcoma of the skin is even rarer, with only few cases well characterized. The authors present 2 cases of this infrequent skin neoplasm. A 76-year-old woman with a nodule on left malar area and an 82-year-old man with a hard nodule on the right temple. First patient's biopsy findings were a dermal lesion mostly composed of malignant osteoid material, with atypical rhabdoid cells intermingled, which was diagnostic of osteoblastic osteosarcoma. Excision of the lesion of the second patient showed a dermal proliferation of atypical spindle-shaped and pleomorphic cells, scattered multinucleated osteoclasts-like cells, and irregular malignant osteoid material. In some fields, atypical cells showed a pseudovascular pattern. Close to this exophytic lesion, a small nest of basal cell carcinoma was observed. Final diagnosis was collision of osteoblastic and telangiectatic primary osteosarcoma and superficial basal cell carcinoma. Both patients have not presented recurrence or metastatic disease after 12 and 9 months of follow-up, respectively. Clinical and histopathologic characteristics of the primary cutaneous osteosarcoma are summarized, and the differential diagnosis of this entity with other benign and malignant skin neoplasms, which can, eventually, show osteoid material.