Abstract 5555: Altered p53/p16 expression is linked to urothelial carcinoma progression but is unrelated to prognosis in muscle-invasive tumors

Abstract Background: Most inactivating p53 mutations result in a nuclear accumulation of the defective p53 protein. However, p53 alterations that result in a complete lack of cellular p53 and complete absence of p53 immunostaining do also occur. As p16 is upregulated in p53 inactivated cells, p16 immunohistochemistry may be a surrogate marker for p53 inactivation. Design: In this study, we investigated p53 and p16 immunostaining on more than 2,500 urothelial bladder carcinomas in a tissue microarray format to better understand their impact in relation to clinicopathological parameters of disease progression and patient outcome. Results: p16 immunostaining was not observed in normal urothelium but occurred in 1,576 (63.5%) of cancers including 755 (30.4%) with a strong staining. The fraction of p16 positive cases increased markedly from pTaG2 low grade (9.6%) to pTaG3 high grade tumors (46.5% strongly positive, p<0.0001 for pTaG2 low vs. pTaG3) but continuously decreased from pTaG3 to pT2 (41.3% strongly positive), pT3 (36.5%) and pT4 (33.3%; p=0.0030). Within pT2-4 carcinomas, p16 positivity was also linked to high grade (p=0.0005) but unrelated to overall survival. p53 staining has been recorded as negative in 203 (8.4%), very weak in 373 (15.4%), weak in 1,341 (55.3%), strong in 115 (4.7%), and very strong in 393 (16.2%) cancers. The fraction of tumors with negative (potentially p53 null phenotype), strong, and very strong p53 positivity increased markedly from pTaG2 low grade to pTaG3 high grade tumors (p<0.0001) and from pTaG3 to muscle-invasive pT2-4 cancers (p=0.0007). p53 staining pattern was unrelated to histopathological parameters of malignancy or patient prognosis within pT2-4 carcinomas, however. There was a significant overall association between p53 and p16 expression but strong p16 expression predominated in tumors with very strong, strong, and negative p53 staining. Subset analyses showed that the combination of p53 negative/p16 strongly positive cancers was particularly linked to features of tumor aggressiveness. Conclusion: Our data show that altered function of p53 and p16 immunostaining increases during grade and stage progression although these alterations lack prognostic significance in pT2-4 carcinomas. That high level p16 expression is limited to neoplastic urothelium and that the p53 null phenotype is largely limited to grade 3 and invasive urothelial carcinomas are features with potential diagnostic utility. Citation Format: Simon Schallenberg, Henning Plage, Sebastian Hofbauer, Kira Kornienko, Sarah Weinberger, Paul G. Bruch, Florian Roßner, Sefer Elezkurtaj, Martina Kluth, Maximilian Lennartz, Tim Mandelkow, Elena Bady, Niclas C. Blessin, Andreas H. Marx, Henrik Samtleben, Margit Fisch, Michael Rink, Marcin Slojewski, Krystian Kaczmarek, Thorsten Ecke, Steffen Hallmann, Stefan Koch, Nico Adamini, Sarah Minner, Ronald Simon, Guido Sauter, David Horst, Tobias Klatte, Thorsten Schlomm, Henrik Zecha. Altered p53/p16 expression is linked to urothelial carcinoma progression but is unrelated to prognosis in muscle-invasive tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5555.