Primary Cutaneous Apocrine Carcinoma and Syringocystadenoma Papilliferum Arising in Nevus Sebaceus: A Case Report and Review of the Literature.

Nevus sebaceus is a hamartomatous lesion characterized by epidermal, follicular, sebaceus, and apocrine gland abnormalities. Approximately 25% of affected individuals may develop benign or malignant secondary neoplasms within the preceding nevus sebaceus. Primary cutaneous apocrine carcinoma (PCAC) is a rare malignant skin tumor affecting elderly adults in their sixth decade of life. Histologically, PCAC appears as a dermal tumor displaying apocrine differentiation with decapitation secretion and malignant features. Secondary malignancy arising from nevus sebaceus is a rare complication, especially for apocrine carcinoma. To date, approximately 200 cases of PCAC have been reported in the literature, and only a few cases have developed PCAC on the scalp. Very few cases (approximately only 12) of PCACs developing in nevus sebaceus have been reported. Here, we report an extremely rare case of the coexistence of PCAC and syringocystadenoma papilliferum arising within nevus sebaceus of the scalp.