Differentiating squamous cell carcinoma from keratoacanthoma using histopathological criteria - Is it possible? A study of 296 cases

Background: Squamous cell carcinoma (SCC) and keratoacanthoma (KA) are some times difficult lo distinguish by histopathological examination, since cyto logical Features are similar in both tumors. Distinctive criteria - mainly architectural - have therefore been proposed as an aid in diagnosis. Object ive: The purpose of this study was to evaluate the reliability of some of t he criteria used to make a distinction between SCC and KA. Methods: 296 ful ly excised tumors previously classified as SCC or KA were randomized and ex amined independently by two examiners. Fourteen criteria, mainly based on t he architecture of the tumors, were determined on the 262 slides for which a consensual diagnosis was made. Results: No single criterion was sufficien tly sensitive and specific to allow a clear-cut differential diagnosis. The 5 most relevant criteria were epithelial lip, sharp outline between tumor and stroma in favor of KA and ulceration, numerous mitoses and marked pleom orphism/anaplasia in favor of SCC. Intraepithelial polymorphonuclear absces ses, intraepithelial elastic fibers, parakeratosis and dyskeratosis and ext ension more lateral than downward were not distinctive criteria, although t hey are considered as classic distinctive features. Conclusion: Many of the criteria commonly used for the differential diagnosis of SCC and KA are no t reliable. The combination of the 5 most useful criteria does not signific antly increase the specificity or sensitivity of the histological diagnosis in difficult cases. Atypical or difficult cases should therefore be consid ered and treated as SCC, since a clear-cut distinction is not possible even with the aid of the most relevant criteria.