Immunohistochemistry for Skin Cancers: A Comprehensive Approach to the Diagnosis of Squamous Cell Carcinoma

Abstract

Background: Squamous cell carcinoma (SCC) is a heterogeneous group of epithelial malignancies with varied morphologies and clinical behaviors. While histopathology is the diagnostic gold standard, it can be limited in distinguishing SCC from morphologic mimics. Immunohistochemistry (IHC) has therefore become a critical adjunct, enhancing diagnostic accuracy and providing prognostic insights. Objective: This narrative review aims to evaluate the diagnostic, differential, and prognostic roles of commonly used IHC markers in SCC, with particular emphasis on their utility in distinguishing SCC from histologic mimickers across different anatomical sites. Methods: One hundred and five peer-reviewed articles were analyzed for their relevance to the immunohistochemical characterization of SCC. Markers were categorized based on their diagnostic function, role in differential diagnosis, and prognostic value. Results: Key markers such as p40, p63, CK5/6, and DSG3 consistently demonstrated high sensitivity and specificity for SCC, reinforcing their value in confirming squamous differentiation. Conversely, exclusion markers like Ber-EP4, CK7, TTF-1, S100, and SOX10 were essential in ruling out basal cell carcinoma, adenocarcinoma, and melanoma. Additionally, markers such as Ki-67, p16, and CD44 offered prognostic information regarding tumor aggressiveness, HPV status, and therapy response. These findings confirm the critical role of IHC not only in diagnosing SCC but also in resolving complex differential diagnoses. Conclusions: IHC markers serve as indispensable tools in the diagnostic workup of SCC, particularly in distinguishing it from other neoplasms with overlapping histologic features. The clear correlation between marker expression and diagnostic categories supports the systematic use of IHC to improve diagnostic precision and inform prognosis. Future integration with molecular diagnostics may further refine personalized treatment approaches in SCC.