Primary cutaneous osteosarcoma of the scalp.

Primary cutaneous extraskeletal osteosarcoma (PCEO) is a rare malignant neoplasm with less than 20 cases reported in the literature to date. Presenting as a nodule or mass on the skin, commonly at sites of previous trauma or radiation, these lesions are differentiated from other neoplasms through their characteristic microscopic appearance. This report highlights a case of PCEO in a 75-year-old man with a history of squamous cell carcinoma (SCC) of the scalp. Histological examination of a scalp nodule in the region of a previously excised SCC revealed proliferation of osteoid surrounded by malignant osteocytes. An overview of this condition and differential diagnoses are presented in this report.