Risk of Breast, Ovarian Cancer Increased in Infertile Women

By Michelle Rizzo NEW YORK JUL 29, 2008 (Reuters Health) - Infertile women have an increased risk of breast and ovarian cancer, although the risk could be related to fertility treatment rather than infertility per se, according to a Danish study published in the July issue of the American Journal of Epidemiology.

"One of the most well-established risk factors for breast, ovarian, and endometrial cancer is parity: Nulliparous women have an increased risk in comparison with parous women," Dr. Allan Jensen and colleagues from the Institute of Cancer Epidemiology, Danish Cancer Society, Copenhagen, write. "A diagnosis of infertility and infertility treatment are related factors also considered to influence risk of these cancers."

The researchers linked data from a large cohort of 54,362 women referred to Danish fertility clinics with information in the Danish Cancer Registry. Using general and parity-specific cancer incidence rates in the general Danish population as a reference, the team assessed cancer risk through standardized incidence ratios (SIRs).

The median length of follow-up was 13 years. Significantly increased SIRs were found for breast and ovarian cancer after adjustment for parity status (SIRs = 1.08 and 1.46, respectively). The risk of breast cancer increased with increasing length of follow-up.

"The increased risk of breast cancer and ovarian cancer after adjustment for parity indicates that other infertility related factors may have the potential to increase the risk of these cancers," Dr. Jensen pointed out in comments to Reuters Health. "Two likely candidates are a shared genetic/biological susceptibility to both cancer and infertility and/or use of fertility drugs."

"Further within-cohort studies are in progress to disentangle the effects of underlying infertility and infertility treatment on cancer risk," the researcher explained. "Furthermore, as our results primarily are based on cancers occurring at a relatively early age, additional follow-up studies are needed to further explore the long-term risk of breast cancer and ovarian cancer among infertile women."

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