Fertility drugs stimulate ovulation and raise estradiol levels, which have been associated with an increased risk of breast cancer. Because results of epidemiologic studies of fertility drugs and breast cancer risk have been inconclusive, researchers from 5 United States sites conducted an extended follow-up study of a cohort of 12,193 women evaluated for infertility between 1965 and 1988. The researchers were able to follow 9,892 women (81.1% of the eligible population) to 2010 by evaluating data and administering questionnaires.
During 30 median years of follow-up, 749 breast cancers were observed. Use of clomiphene citrate among 38.1% of women was not associated with an increased risk of breast cancer. However, the risk was higher for women who received multiple cycles, with the risk for invasive cancers confirmed by medical records being significantly elevated. This risk remained relatively unchanged after adjustment for causes of infertility and multiple breast cancer predictors. Gonadotropins, used by 9.6% of women, usually in conjunction with clomiphene, showed inconsistent associations with risk, although a significant relationship of use with invasive cancers was seen among women who remained nulligravid. The researchers concluded that since their study focused on a young population of women, additional evaluation of long-term fertility drug effects on breast cancer is warranted.
Brinton LA, Scoccia B, Moghissi KS. Long-term relationship of ovulation-stimulating drugs to breast cancer risk. Cancer Epidemiol Biomarkers Prev; 2014: 23(4); 584–93.