Body mass index modifies bladder cancer risk associated with low estrogen exposure among Egyptian women after menopause

Purpose Investigators have reported inconsistent findings regarding associations between body mass index (BMI) and bladder cancer risk, and they have postulated that sex steroids mediate such associations. We assessed the impact of BMI on the relationship between bladder cancer risk and combinations of age at first childbirth, parity, and age at menopause, among Egyptian women. Methods We used data from our multicenter case–control study of 419 cases and 786 controls in logistic regression models to estimate adjusted odds ratios (AORs) and 95% confidence intervals (CIs) of such associations. Results Age > 18 years at first childbirth and parity ≤ 6 were significantly associated with bladder cancer risk, which was higher when both factors (AOR = 2.31, 95% CI = 1.55–3.43) and age at menopause < 45 years (AOR = 3.51, 95% CI = 1.88–6.55) were present. Early menopause was associated with higher bladder cancer risk in obese (AOR = 2.90, 95% CI = 1.40–5.98) but not normal weight women (AOR = 0.98, 95% CI = 0.58–1.65; P interaction = 0.11), and the risk was greatest when both first childbirth at age > 18 years and parity ≤ 6 were present (AOR = 7.60, 95% CI = 1.84–31.35); however, overweight and obesity were associated with significantly lower bladder cancer risk (AOR = 0.59, 95% CI = 0.43–0.81, and AOR = 0.26, 95% CI = 0.18–0.38, respectively). Conclusion Body mass index appears to modify bladder cancer risk in Egyptian women after menopause by slightly enhancing the risk associated with low estrogen exposure among the obese only. Longitudinal studies of the BMI role in bladder malignancy in this distinctive population are required.