2025 Volume 40 Issue 1 Pages 17-22
An 83－year－old female presented with a nodule on the right lower leg two months before the first medical examination. Biopsy suggested seborrheic keratosis (SK) ; however, malignancy remained suspected, prompting complete excision. Histopathology revealed peripheral features consistent with SK, but there was a central crateriform area with pleomorphism and nuclear atypia, indicating squamous cell carcinoma (SCC). Immunohistochemically, p16 and p53 were negative in the regions with SK but positive in the SCC in situ, adjacent to the center. In contrast, invasive SCC at the center was strongly p53 positive but p16 negative, suggesting a stepwise malignant transformation from SK to SCC in situ, and ultimately to SCC. Involvement of human papilloma viru s was not clearly identified. This case highlights the possibility of malignant changes in patients with SK. A review of the relevant literature on the pathogenesis and clinical implications of such transformations will also be presented.[Skin Cancer (Japan) 2025 ; 40 : 17－22]
