Fertility Tx May Alter Cancer Risk

The unsuccessful use of fertility drugs was associated with a reduced risk of young-onset breast cancer, although women who did go on to conceive saw an increased risk for the disease, according to researchers.

In a retrospective sister-matched case-control study, women who had used fertility drugs but had not conceived a 10-plus-week pregnancy under treatment showed a statistically significantly decreased risk of breast cancer compared with nonusers (OR 0.62, 95% CI 0.43 to 0.89), reported Clarice Weinberg, PhD, from the National Institute of Environmental Health Sciences in Research Park Triangle, N.C., and colleagues.

Also, women who had used any fertility drugs showed a nonstatistically significant decreased risk of breast cancer, compared with nonusers (OR 0.82, 95% CI 0.63 to 1.08), they wrote in the July 6 Journal of the National Cancer Institute.

However, women who had used fertility drugs and conceived a 10-plus-week pregnancy did have a statistically significantly increased risk of breast cancer compared with women who had been unsuccessfully treated.

"Our data suggest that exposure to a stimulated pregnancy is enough to undo the reduction in risk associated with a history of exposure to ovulation-stimulating drugs," the group wrote.

The widespread use of ovulation-stimulating fertility drugs has raised concerns about their link to breast cancer, but results from previous research have been too varied to make a definitive connection.

A recent meta-analysis of published studies was inconclusive because of methodological limitations, such as incomplete control for confounding and small numbers of case subjects (Breast Cancer Res Treat 2010; 124: 13–26.)

The current Two Sister Study included women diagnosed with breast cancer (1,422) under the age of 50 years, and their breast cancer-free control sisters (1,669). They were studied between September 2008 and December 2010. The mean age of control sisters was 47.7 years at enrollment, and the mean age of case sisters was 44.7 years at diagnosis.

Participants were asked about fertility medication usage, the type of fertility medication, when they began the medication, the number of menstrual cycles of use, and whether any treatment had resulted in a pregnancy lasting 10 or more weeks. Fertility-drug use was categorized as: nonuser; clomiphene citrate (CC) only; follicle-stimulating hormone (FSH) only; or both CC and FSH.

The researchers found that women who reported use of CC alone, or both CC and FSH, without any success showed a nonstatistically significantly reduced odds of young-onset breast cancer compared with nonusers of these drugs:

CC only: OR 0.61, 95% CI 0.41 to 0.90
CC and FSH: OR 0.53, 95% CI 0.29 to 0.96

Women who had used fertility drugs and conceived a 10-plus week pregnancy under treatment showed a statistically significant increased risk of breast cancer compared with unsuccessfully treated women (OR 1.82, 95% CI 1.10 to 3.00).