Abstract 17: Sex disparities in a murine model of BBN-induced bladder cancer

Abstract Bladder cancer is one of the most common cancers in the US, with an estimated incidence of 83,730 cases in 2021. Males are four times more likely to develop bladder cancer than females. Ninety percent of cases are diagnosed as urothelial carcinomas, and most cases are not muscle-invasive at the time of diagnosis. Even with treatment, there is a 50-80% chance of bladder cancer recurrence within five years of diagnosis. While non-invasive disease has a five-year survival rate of 77%, if recurrence leads to metastatic disease, the five-year survival rate is only 6%. Therefore, there is a need to predict which patients will recur and progress to metastatic disease. N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) is a cigarette smoke-mimicking carcinogen that can be used in mice to induce urothelial cell proliferation and progression to invasive bladder cancer. This study used a BBN-induced bladder cancer model to evaluate sex differences in urothelial proliferation and bladder pathologies in male and female mice treated with BBN (0.05%) in their drinking water for up to 12 weeks. Mice were then given a 2–20-week period of no treatment following BBN exposure. Bladder specimens were stained with Ki-67 to analyze urothelial proliferation and characterized based on pathology. Male bladder samples characterized as having reactive atypia showed greater proliferation rates than male bladder samples with urothelial dysplasia. Overall, compared to female bladder samples, male bladders showed greater urothelial proliferation in both reactive atypia and dysplasia categories. Additionally, male mice had more tumor initiation and aggressive disease at all examination timepoints, with the most pronounced difference seen at 10-weeks post-BBN exposure. The development of carcinoma in situ (CIS) and invasive disease was seen in 100% of males at 12 weeks post-BBN, while only 40% of female mice had CIS or invasive disease at the same timepoint. Overall, these findings indicate that mouse sex plays a role in bladder tumor progression, with females having delayed tumor initiation and less aggressive disease. This may be due, in part, to varied immune cell profiles in males versus females. A short 2-week exposure to BBN caused a similarly profound neutrophil and macrophage infiltrate in the bladder of both sexes but no changes in immunosuppressive populations such as regulatory T cells (Tregs). In stark contrast, a 12-week exposure to BBN with a 2-week rest period resulted in significantly more macrophages and immunosuppressive PD-L1+ neutrophils and Tregs in the bladders of male mice when compared with females. Chronic exposure to BBN leads to an increase in immunosuppressive immune infiltrates in male bladders and may contribute to sex disparities observed in bladder cancer. Citation Format: Gabrielle E. Kennelley, Jordan J. McDonald, Norbert Sule, Barbara A. Foster, Craig M. Brackett, Wendy J. Huss. Sex disparities in a murine model of BBN-induced bladder cancer [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 17.