Abstract 6509: Carcinogen withdrawal in the BBN induced mouse model of bladder cancer mimics cigarette smoking cessation in humans with decreased tumor progression

Abstract Field cancerization is associated with greater tumor mutational burden in bladder cancer. Mutations in TRP53 (p53) are early drivers of disease and correlate with tumor stage, grade, and a poor prognosis. In humans, cigarette smoking correlates with a greater frequency of p53 mutations. N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) is a cigarette smoke-mimicking carcinogen that can be used to induce bladder cancer in rodent models. Mirroring real-world phenomena, BBN exposure induces p53 mutations and leads to more rapid tumor initiation and progression in male rodents. Male and female mice were exposed to 0.05% BBN in drinking water for 4, 12, or 20 weeks (wks). Bladder samples were collected immediately after BBN discontinuation or after a period of drinking untreated water. Pathology, proliferation, and mutant p53 expression were analyzed to investigate BBN-induced field cancerization in urothelium, urothelial carcinoma in situ (UCIS), and invasive urothelial carcinoma (iUC). Mice exposed to 4 wks of BBN had groups of proliferative and mutant p53 cells. A continuous basal proliferation pattern was more commonly seen in males compared to females (87% vs. 43%), and a single male progressed to UCIS. Interestingly, by 22 wks (18 wks untreated drinking water after 4 wks BBN), there was no longer detectable proliferation, mutp53 cells, or UCIS. Mice exposed to 12 wks of BBN progressed to UCIS or iUC (55% males vs. 33% females). Most bladders with UCIS had a continuous basal cell proliferation pattern with mutant p53. By 22 wks (10 wks untreated drinking water after 12 wks BBN), bladders with UCIS had limited continuous basal cell proliferation but retained mutant p53, and males had more iUC than females (38% vs. 14%). Additionally, by 52 wks (40 wks untreated drinking water after 12 wks BBN), males more often progressed to iUC compared to females (94% vs. 44%). By 78 wks (66 wks untreated drinking water after 12 wks BBN), 75% of females progressed to iUC. After 20 wks of BBN, all male mice progressed to iUC by 26 wks, whereas iUC development in female mice was delayed until 51 wks. BBN induces p53 mutations associated with the initiation and progression of murine bladder cancer. Data showing mutant p53 without development of UCIS or iUC in mice treated with BBN for 4 wks indicates field cancerization is not maintained after a short exposure to BBN. However, exposure to BBN for 12 wks induces iUC in most males, but less in females, and 20 wks of BBN exposure leads to more rapid iUC development in males than in females. This data mimics research in humans showing a reduced risk of bladder cancer development after cessation of cigarette smoking. The pattern of mutant p53 staining, particularly p53 mutations within proliferating cells, may also correlate with greater field cancerization and likelihood of UCIS and iUC development, particularly in those with a longer history of carcinogen exposure. Citation Format: Gabrielle Kennelley, Alexandra Pado, Rachel Sanyu, Norbert Sule, Craig Brackett, Barbara Foster, Wendy Huss. Carcinogen withdrawal in the BBN induced mouse model of bladder cancer mimics cigarette smoking cessation in humans with decreased tumor progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6509.