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Case Reports

Abstract

Nevus sebaceous (NS) is a type of congenital epidermal nevus characterized by a hamartoma resulting from the abnormal proliferation of the pilosebaceous follicular unit, which contains epidermal, apocrine, and sebaceous elements. Various secondary neoplasms are known to arise from NS, most of which are benign. Trichoblastoma and syringocystadenoma papilliferum are the most common, but occasionally, malignant tumors can also develop from NS. Infrequently, multiple secondary tumors can occur within a single NS. However, the occurrence of six or more neoplasms arising from an NS is extremely rare. Here, we report a case of likely NS in a 66-year-old male with eight closely admixing and intermingled secondary neoplasms, including a malignant neoplasm, basal cell carcinoma. Knowledge about NS with secondary neoplasms is limited to a few case reports; however, all previously documented cases of NS with seven or more secondary tumors did not involve a malignant entity. The histologic pattern exhibits a unique feature of intermingled various neoplasms, which appear to be hybrid and interconnected. Although the patient did not have a documented diagnosis of NS prior to surgery, he confirmed the presence of the lesion for many years, and examination of the background skin showed features consistent with an old NS, such as apocrine glands. This case highlights that epithelial, adnexal, and follicular neoplasms can arise simultaneously from a nevus sebaceous. By presenting this case and reviewing all published NS cases with multiple secondary neoplasms, we aim to expand knowledge about the biological and clinical behavior of this rare phenomenon.