Medial Canthal Collision Tumor with Seborrheic Keratosis Hiding Underlying Basal Cell Carcinoma
A 74-year-old man presented with a 3-year history of a tan papule on his right medial canthus (A). Excisional biopsy showed basket-weave hyperkeratosis (B, arrowhead), acanthosis (C, double-headed arrow), papillomatosis with squared fronds (C, ∗), and horn pseudocysts (D, ★) overlying nests of peripheral palisading atypical basaloid cells with surrounding retraction artifact (E, arrows), indicative of a collision tumor consisting of an overlying seborrheic keratosis (SK) and an underlying nodular-type basal cell carcinoma (BCC).