Secondary neoplasms in nevus sebaceous can develop during adolescence and adulthood. Trichoblastoma and syringocystadenoma papilliferum are the most common benign neoplasms, but poroma is rarely reported. A 28-year-old female presented with an asymptomatic mass on the scalp. She has had a hairless lesion on the scalp since birth. A soft mass developed on that lesion four years prior. Physical examination revealed a localized 1 cm×2.5 cm-sized brownish, verrucous-surfaced plaque with a 1 cm×1 cm-sized pedunculated erythematous tumor on the scalp. We performed skin biopsy on both the plaque and tumor lesions. The histopathological findings demonstrated the plaque lesion consistent with nevus sebaceous and the tumor lesion consistent with eccrine poroma. Surgical mass excision was performed. The patient was eventually diagnosed with eccrine poroma arising within nevus sebaceous. To the best of our knowledge, there are only six reported cases on poroma arising within nevus sebaceous. Although rarely documented in the literature, it should be considered as a secondary neoplasm within nevus sebaceous.
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