Clinical and histopathological characteristics of patients with cutaneous squamous cell carcinoma arising within seborrheic keratosis

Abstract

Seborrheic keratosis (SK) is a common benign cutaneous neoplasm; however, rare cases of malignant transformation to squamous cell carcinoma (SCC) have been reported. This study aimed to investigate the clinical and histopathological characteristics of SCC arising within SK (SCC-SK). We retrospectively reviewed 360 SCC lesions in 345 patients treated at a single institution between October 2014 and December 2022. Two definite SCC-SK cases (0.56% of all SCC lesions) were identified among 360 SCC lesions, together with one additional probable case in which SCC developed at the same site as biopsy-proven SK 6 years earlier, yielding an overall frequency of 0.83%. All patients were in their 90s at diagnosis, and two were immunosuppressed. The tumors were located in sun-exposed areas, including the preauricular region, scalp, and cheek. Patient 2 developed lymph node metastasis, whereas the other two patients remained disease-free. In Patient 3, EMA immunostaining showed diffuse tumor-cell positivity without a ductal or luminal pattern; together with keratinizing squamous morphology and horn pearl formation, these findings favored SCC over eccrine porocarcinoma. SCC-SK should be considered in enlarging or atypical SK-like lesions, particularly in older or immunosuppressed patients.