Abstract

Keratoacanthoma (KA) most commonly presents as a crateriform lesion on the sun-exposed areas of the skin. Clinically it is characterized by three chronological stages: an initial rapid growth stage, a fully developed stage and a final regression stage. Despite remaining controversial, it is generally considered a borderline squamous neoplasm. Recent studies have suggested that in addition to the UV-associated mutational signature, different molecular signaling pathways such as p53, wingless-INT (Wnt), Notch and mitogen-activated protein kinases (MAPK) can be involved. Here we reviewed histopathology slides of a total of 143 KA cases from a dermatopathology-specialized reference lab. Diagnoses of all KA cases have been confirmed and deemed to be clinicopathologically correlated. Architectural features such as papillomatosis, hyperkeratosis, parakeratosis, hypergranulosis, microabscess formation and cytological features such as koilocytic changes, dyskeratosis, degree of atypia and mitotic counts were taken into account. All the reviewed KA cases were classified into nine major patterns accordingly, i.e., 1) classic, 2) solid, 3) cystic, 4) microabscess-rich, 5) verruciform, 6) irritated seborrheic keratosis (ISK)-like, 7) prurigo-like, 8) basaloid and 9) squamous cell carcinoma (SCC)-like. These benchmarked morphological patterns may be suggestive of unique correlation with molecular alterations and therefore shed light on their underlying etiologies. It also has the potential to predict clinical outcome especially the course and regression tendency.