Parity, early menopause and the incidence of bladder cancer in women: a case-control study and meta-analysis

Abstract

Introduction: Incidence rates of bladder cancer are notably higher in men than in women. While there is evidence that reproductive and hormonal risk factors may influence risk of bladder cancer, data are inconclusive.

Materials and methods: We examined reproductive, menstrual and hormonal use history in our population-based case-control study of bladder cancer in New Hampshire (NH), USA (n=207 women cases and n=463 women controls). Additionally, we performed a meta-analysis of the published literature. We used unconditional logistic regression analysis to compute adjusted odds ratios associated with each risk factor in the NH study. We combined these estimates with those from the published literature using inverse variance effects models.

Results: In the NH study, a slightly decreased odds ratio was found among women who had ever had a birth compared to nulliparous women and an elevated odds ratio among women who underwent surgical menopause (bilateral oophorectomy), especially at an early age. No overall associations were found with oral contraceptive use or hormone replacement therapy. These findings were generally in agreement with the meta-analytic results for which the combined relative risk (RR) estimate was reduced among ever parous women (combined RR estimate for ever parous versus nulliparous=0.66, 95% confidence intervals [95% CI] 0.55-0.79) and elevated among those undergoing an early menopause (combined RR estimate for early versus late menopause=1.59, 95% CI 1.31-1.92). No consistent risk was observed for the other factors.

Discussion: Some reproductive and menstrual factors appear to be related to the incidence of bladder cancer among women; but whether effects are due to female hormones is uncertain.

Figure 1. Meta-analysis forest plot of parity and bladder cancer risk in women

For individual studies, the center of the circle represents the individual study relative risk estimate and the radius of the circle being proportional to the weight of the study relative risk estimate in the summary relative risk (RR) computation (reciprocal of the variance)–. The line represents the confidence interval. The combined RR estimate derived from the meta-analysis is represented by a diamond, with the 95% confidence interval represented by the bold line.

Figure 2. Meta-analysis forest plot of early menopause and bladder cancer risk in women

For individual studies, the center of the circle represents the individual study relative risk estimate and the radius of the circle being proportional to the weight of the study relative risk estimate in the summary relative risk (RR) computation (reciprocal of the variance)–. The line represents the confidence interval. The combined RR estimate derived from the meta-analysis is represented by a diamond, with the 95% confidence interval represented by the bold line.