Oral contraceptives associated with prostate cancer incidence

Canadian researchers report a significant association between oral contraceptive (OC) use and the incidence of prostate cancer in a study published online November 14 in BMJ Open.
 
Following up on several previous studies suggesting that exposure to estrogen may raise the risk of prostate cancer, researchers from the Princess Margaret Hospital in Toronto investigated whether estrogen from OCs contaminates the environment (eg, through the water supply) leading to low-level exposure and increased cancer risk. They correlated global data on age-standardized rates of prostate cancer and related deaths in 2007 from the International Agency for Research on Cancer with information on the percentage of women using Ochs and other contraceptive methods from the United Nations World Contraceptive Use 2007 report, analyzing the data by country and continent. Analysis found a significant association (P<0.05) between OCs and prostate cancer incidence and mortality in individual nations worldwide and by continent. No such association was seen for other contraceptive methods.

The effect of OCs “may be mediated through environmental oestrogen levels; this novel concept is worth further investigation,” the authors write. They note that “classic case-control and cohort studies may not reveal this association as we are hypothesising an environmental effect” and urge additional environmental and tissue correlation studies.

Further analysis of the data revealed that the association between OC use and prostate cancer was independent of a country’s wealth. However, additional confounding factors exist and should be explored, the researchers say. They also note that data on true levels of endocrine-disturbing compounds in the water supply and food chain currently aren’t available.

Although the study doesn’t prove cause and effect, the authors speculate that because OCs often contain high doses of ethinyloestradiol, which is “excreted in urine without degradation,” it “can then end up either in the drinking water supply or passed up the food chain.”

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