Bladder cancer is the fifth most frequent tumor in men and ninth in women in the United States. Due to a high likelihood of recurrence, effective chemoprevention is a significant unmet need. Estrogen receptors (ERs), primarily ERβ, are expressed in normal urothelium and urothelial carcinoma, and blocking ER function with selective ER modulators such as tamoxifen inhibits bladder cancer cell proliferation in vitro. Herein, the chemoprotective potential of tamoxifen was evaluated in female mice exposed to the bladder-specific carcinogen, N -butyl-N -(4-hydroxybutyl) nitrosamine (BBN). Carcinogen treatment resulted in a 76% tumor incidence and increased mean bladder weights in comparison to controls. In contrast, mice receiving tamoxifen concurrent (8-20 weeks) or concurrent and subsequent (8-32 weeks) to BBN administration had no change in bladder weight and only 10% to 14% incidence of tumors. Non-muscle-invasive disease was present in animals treated with tamoxifen before (5-8 weeks) or after (20-32 weeks) BBN exposure, while incidence of muscle-invasive bladder carcinoma was reduced. ERβ was present in all mice and thus is a potential mediator of the tamoxifen chemoprotective effect. Surprisingly, ERα expression, which was detected in 74% of the mice exposed to BBN alone but not in any control mice, was correlated with tumor incidence, indicating a possible role for this receptor in carcinogen-induced urothelial tumorigenesis. Thus, these data argue that both ERα and ERβ play a role in modulating carcinogen-induced bladder tumorigenesis. Administration of tamoxifen should be tested as a chemopreventive strategy for patients at high risk for bladder cancer recurrence.Translational Oncology (2013) 6, 244-255
IntroductionAs the fifth most common cancer in men and ninth most common in women in the United States, urinary bladder cancer accounts for significant morbidity and mortality. There are estimated to be more than 73,000 new bladder cancer cases in 2012 [1] with urothelial carcinoma accounting for approximately 90% of these; the remainder is composed of squamous cell carcinomas, adenocarcinomas, and other rare histologies [2]. Approximately 70% of all new bladder cancer cases are classified as non-muscle-invasive (Ta, T1, Tis), while the remaining 30% are muscle-invasive (T2-T4) and generally lead to cystectomy. Bladder cancer recurs at a very high rate of 50% to 90% depending on the tumor stage, grade, and number of primary tumors, and this necessitates lifetime monitoring for tumor recur-