A pilot study of p53 immunohistochemistry in atypical squamous lesions, using a vulvar scoring system

Background: Histopathologic overlap between cutaneous squamous cell carcinoma (cSCC) and its indolent mimics likely leads to the overdiagnosis of cSCC. ObjectiveTo perform a pilot study of the p53 immunohistochemical scoring system developed on vulvar squamous lesions in cSCC. Methods: The consistency and reliability of p53 immunostaining using a scoring system developed on vulvar cases, as compared with TP53 genomic sequencing, was studied in an initial cohort of 28 cutaneous cases. p53 labeling was further assessed in an additional 63 cases of atypical squamous lesions, including 20 atypical squamous lesions classified by the authors as benign, 22 cases diagnosed as cSCC without high-risk features, and 21 cases of high-risk cSCC (cSCC-HR). Results: The concordance of p53 labeling and TP53 sequencing was 82.1%. Four positive patterns of p53 mutation were identified: basal, parabasal/diffuse, null, and cytoplasmic. p53 positivity in atypical, benign squamous lesions (10%) was significantly lower than that of low-risk cSCC (63.6%, p = 0.0004) or cSCC-HR (90.5%, p < 0.0001). p53 positivity in low-risk cSCC versus cSCC-HR was not statistically significant (p = 0.07). Conclusionp: 53 Labeling may be a helpful biomarker to support the diagnosis of cSCC and distinguish cSCC from atypical but benign mimics.