P53 in Penile Squamous Cell Carcinoma: A Pattern-Based Immunohistochemical Framework with Molecular Correlation

SIMPLE SUMMARY: Penile squamous cell carcinomas harbouring mutations of TP53 have an increased risk of lymph node metastases and an impaired prognosis, but the mutational analysis of the TP53 gene is not available in many pathology laboratories. Although p53 immunohistochemistry (IHC) has been proposed as an alternative to the molecular analysis, the current method of evaluation of p53 IHC has many inaccuracies. The aim of our study was to determine, in a series of 40 penile tumours, if a recently described pattern-based framework of p53 IHC evaluation correlates better than the classical method with the TP53 mutational status. Our results show that the new method has a very good correlation with TP53 mutations (95% sensitivity; 92% specificity), higher than that of the classical method, and can be considered as a reliable surrogate of the TP53 mutational status. This new framework can help clinicians to better define risk groups and refine treatment strategies. ABSTRACT: p53 immunohistochemistry (IHC) has been proposed as a surrogate for TP53 mutations in penile squamous cell carcinomas (PSCC). We aimed to evaluate the performance of a pattern-based evaluation of p53 IHC in PSCC. Human papilloma virus (HPV) DNA testing, p16 and p53 IHC, and whole exome sequencing were performed in a series of 40 PSCC. p53 IHC was evaluated following a pattern-based framework and conventional p53 IHC evaluation. Out of 40 PSCC, 12 (30.0%) were HPV-associated, and 28 (70.0%) were HPV-independent. The agreement between the p53 IHC pattern-based evaluation and TP53 mutational status was almost perfect (k = 0.85). The sensitivity and accuracy of the pattern-based framework for identifying TP53 mutations were 95.5% and 92.5%, respectively, which were higher than the values of conventional p53 IHC interpretation (54.5% and 70.0%, respectively), whereas the specificity was the same (88.9%). In conclusions, the pattern-based framework improves the accuracy of detecting TP53 mutations in PSCC compared to the classical p53 IHC evaluation.