Rare Secondary Neoplasms Arising in Epidermal Nevus: A Case Series and Literature Review.

Malignant transformation is known to occur with many nevi, such as nevus sebaceus. However, cases of secondary tumors developing in an epidermal nevus (EN) are rare, with only a few case reports documented in the literature. We present three unique cases of syringocystadenoma papilliferum (SCAP), syringofibroadenoma, trichilemmoma, and basal cell carcinoma (BCC) arising in EN. The first case is a 40-year-old female who presented with a verrucal plaque extending from mons pubis to the left lateral thigh since birth. Histologic examination revealed EN with areas of syringofibroadenoma, SCAP, and BCC. The second case is a 31-year-old male who had EN since birth on his left axilla, trunk, and buttock. Over time, several verrucous pink nodules developed on these areas. Microscopic evaluation of these nodules demonstrated characteristic features of SCAP and trichilemmoma. The third case is a 29-year-old female who developed a suspicious flesh-colored papule within a pre-existent EN on her left knee. Upon excision, the papule was diagnosed as a trichilemmoma. The occurrence of epithelial/adnexal tumors in EN remains elusive as to whether these lesions are clonally related or simply independent tumors that have coincidentally collided. We highlight the importance of considering the development of secondary neoplasms in the setting of EN, underscoring the need for regular patient follow-up.