A Case of Basal Cell Carcinoma arising in Seborrheic Keratosis

Malignant tumor occurring within seborrheic keratosis (SK), which is one of the most common benign cutaneous tumors, is very rare. Basal cell
carcinoma (BCC), squamous cell carcinoma and malignant melanoma have been previously documented to occur within SK, and BCC is the most
common malignant neoplasm occurring with SK. A 66-year-old woman presented with recurrent, localized, well-demarcated, verrucous reddish
nodule on left forearm. After wide excision, the histopathological study of the 2.0 x 1.2 x 0.7 cm sized lesion revealed atypical nodular pigmented
basaloid cellular proliferation with acanthosis and some peritumoral clefts conjunction to basal epidermal layer. The CK19 stain showed weakly
and diffusely positive reaction for the pigmented lesion, and the overexpression of p53 protein was moderately observed in the specimen. Finally,
the patient was diagnosed with BCC. Herein, we report a rare case of the development of BCC in SK. It is important to note that most BCC arise
sporadically (de novo), without a preceding skin lesions or family history, but cases of malignant changes in seborrheic keratosis also increasingly
reported worldwide as well as this case. Considering the incidence of BCC increases on the sun exposed area of skin of Asian populations, there is
an educational significance and purpose that clinicians need intensive examinations for similar skin lesions.