Squamous cell carcinoma of the anus: morphological evaluation and ancillary techniques

Background: the present study deals with anal carcinoma, focusing on morphological evaluation, histopathological characteristics, and immunophenotypic profile, as well as the incidence, risk factors, and molecular profile of this pathology, underlining the importance of a correct differential diagnosis. Materials and Methods: this study was conducted in the laboratory of Anatomic Pathology at the Santa Rita Clinic, Monza Policlinic Group, located in Vercelli. We collected samples of 13 anal biopsies with a diagnosis of squamous cell carcinoma of the anus, referred from April 2022 to February 2025. A retrospective analysis was performed on paraffin-embedded Hematoxylin and Eosin (H&E) and immunohistochemical samples. The study contributed to expanding the case history present in the literature and allowed for a review of the differential diagnostic criteria in light of the immunophenotypic expression of neoplastic subtypes. The morphological analysis was performed by microscopic observation of the hematoxylin and eosin-stained specimen slide, while immunophenotypic analysis was performed by immunohistochemical staining of the specimen with specific antibodies (anti-pan keratin, anti-keratin, anti-CK8/18, anti-CK7, anti-p16INK4a, anti-p40, GATA3, anti-chromogranin A, anti-synaptophysin) and subsequent microscopic examination. Morphological analysis allowed for the identification of histotypes, while immunohistochemical analysis allowed for a differential diagnosis with other anal canal tumors. Results: from the analysis of the case history, it was seen, in agreement with other previous studies, that this pathology is rare, as it is found in 3% of biopsies of the anal region, that it has a higher incidence in females, and, in the majority of cases, the neoplasm is related to Human Papillomavirus (HPV) infection. Conclusions: anal squamous cell carcinoma is a rare but increasing neoplasm, with variable histological characteristics that can lead to misdiagnosis. Therefore, a correct differential diagnosis through analysis of morphology and immunophenotypic expression is essential. HPV infection is a significant risk factor, and vaccination in at-risk populations could reduce its incidence.