title: Nodulocystic Basal Cell Carcinoma Arising Directly from a Seborrheic Keratosis: A Rare Case Report.
abstract: Seborrheic keratoses (SKs) are common epidermal tumors composed of benign keratinocytes. Malignant skin tumors including basal cell carcinoma (BCC) rarely arise within SKs. We report a rare case of an 82-year-old man with nodulocystic BCC that appeared at the center of a scaly hyperpigmented SK that had been presented for more than 10 years. It was histologically confirmed that CK19-positive BCC arose directly from the wall of the pseudohorn cyst, a part of the SK. Nodular and/or cystic BCC also rarely arise within SKs while the most common histologic type of BCC within SKs is the superficial type. Careful observation of SKs is important even though it is rarely a background condition for malignant transformation.
authors: Department of Dermatology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors: Kana
authors: K
authors: Shibao
authors: Department of Dermatology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors: Naoko
authors: N
authors: Okiyama
authors: Department of Dermatology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors: Ryota
authors: R
authors: Tanaka
authors: Department of Dermatology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors: Hitoshi
authors: H
authors: Maruyama
authors: Department of Dermatology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors: Yasuhiro
authors: Y
authors: Fujisawa
authors: Department of Dermatology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors: Manabu
authors: M
authors: Fujimoto
keywords: Basal cell carcinoma; CK19; pseudohorn cyst; seborrheic keratosis