Cancer Research Lab

Younger age at menopause is associated with an increased risk of bladder cancer, researchers from the University of Minnesota School of Public Health in Minneapolis report.

Bladder cancer is common in the U.S., representing about 6% of all new cancer cases among men and 2% among women, Anna E. Prizment and colleagues report in the March issue the International Journal of Cancer. “Established risk factors for bladder cancers include age, gender, smoking and chemical carcinogens.”

The researchers examined the association between reproductive factors and bladder cancer in a prospective cohort study of 37,459 women (between the ages of 55 and 69 years) from Iowa. The women were initially free from cancer in 1986. The participants reported reproductive history and were followed through 2003.

During follow-up, a total of 192 women (0.5%) were diagnosed with bladder cancer at an average age of 73 years. An inverse association was observed between age at menopause and incident bladder cancer after adjusting for age and smoking.

Compared with women who reached menopause at age 48 or later, the hazard ratio (HR) of bladder cancer was 1.32 for women who reached menopause between 43 and 47 years, and 1.60 for those younger than 42 years (p for trend = 0.02). These associations were comparable for natural and surgical menopause.

The risk of bladder cancer was also increased among women with a history of bilateral oophorectomy compared to those who did not undergo bilateral oophorectomy (HR = 1.58) and the researchers noted a trend between bladder cancer and fewer lifetime years of ovulation.

No associations were found between bladder cancer and any other reproductive factors including age at menarche, age at first birth, number of births, hormone replacement therapy use, infertility, fibroid tumors, ovarian cysts or endometriosis.

“Earlier it was suggested that the deficiency of endogenous estrogen after menopause could lead to an increased number of urinary tract infections associated with bladder cancer,” Prizment said “This may explain why we observed associations between bladder cancer and only those reproductive factors which were related to menopause.”

However, Prizment added: “It is too early to make any definite conclusions since the biological mechanism of this association is unclear.”