To examine the association between fertility drug use and young-onset breast cancer, Chunyuan Fei, Ph.D., from the National Institute of Environmental Health Sciences in Research Triangle Park, N.C., and colleagues conducted a sister-matched case-control study that included 1,422 cases who were younger than age 50 years at diagnosis with breast cancer, enrolled within four years of diagnosis, and 1,669 breast cancer-free control sisters.

The researchers found that 288 participants reported using ovulation-stimulating drugs (193 clomiphene citrate only; 29 follicle-stimulating hormone only; 66 both). Compared with nonusers, women who had used fertility drugs had a nonsignificantly decreased risk of breast cancer (odds ratio [OR], 0.82; 95 percent confidence interval [CI], 0.63 to 1.08). Compared with nonusers, women who had used fertility drugs but had not conceived a 10+ week pregnancy had a significantly decreased risk of breast cancer (OR, 0.62). Compared with unsuccessfully treated women, women who had conceived using fertility drugs had a significantly increased risk of breast cancer (OR, 1.82); their risk was similar to women who had not used fertility drugs (OR, 1.13; 95 percent CI, 0.78 to 1.64).

"In this sister-based case-control study, a history of unsuccessful use of ovulation-stimulating fertility drugs was associated with a statistically significantly reduced risk of young-onset breast cancer, but the occurrence of a stimulated 10+ week pregnancy appeared to offset the protective association," the authors write.

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