Case of seborrheic keratosis with underlying basal cell carcinoma suggesting a collision tumor.

Reports of seborrheic keratosis (SK) with concurrent malignant tumors are rare, but previous and recent reports - especially the co-manifestation of basal cell carcinomas (BCC) have added to the ongoing debate of the possibility of the development of BCC from SK. We report a rare case of SK with underlying BCC with scarcely accounted histopathological characteristics - reticulated type and nodular type, respectively - that showed no direct histological link between the two entities. We also carefully suggest that differences in histopathology (whether the two lesions are connected or not) may account for the possibility of incidental co-habitation.