Fertility Drugs Do Not Increase Long-Term Breast Cancer Risk, Study Finds
Patients followed for 30 years in large-scale analysis
Nearly 10,000 women who received fertility drugs to stimulate ovulation were no more likely to develop breast cancer during 30 years of follow-up than were those who never used the drugs, according to a study published in the April 2014 edition of Cancer Epidemiology, Biomarkers & Prevention.
Previous reports had raised concerns because women are exposed to higher levels of estrogen during fertility treatments. Extended exposure to extra estrogen could increase the risk of breast cancer.
In the new study, researchers conducted an extended follow-up among 12,193 women who were evaluated for infertility between 1965 and 1988 at five U.S. sites. Follow-up through 2010 was achieved for 9,892 women (81.1% of the eligible population).
During a median follow-up period of 30 years, 749 breast cancers were observed.
The investigators found that the use of clomiphene citrate among 38.1% of the patients was not associated with a risk of developing breast cancer (hazard ratio [HR], 1.05). However, somewhat higher risks were seen for patients who received multiple cycles of the drug. In a small subset of women who were exposed to 12 or more cycles of clomiphene treatment, the risk of developing breast cancer was 70% higher than that in women who were not exposed.
The overall lack of a risk of breast cancer remained unchanged after the researchers adjusted for causes of infertility and multiple breast cancer predictors.
Gonadotropins, used by 9.6% of patients (mainly in conjunction with clomiphene), showed inconsistent associations with breast cancer risk, although a significant relationship of use with invasive cancers was seen among women who remained nulligravid. This subset of patients was about twice as likely to develop breast cancer (HR, 1.98).
The authors caution that continued study of women who receive fertility treatments is needed because many women included in the new analysis were fairly young (in their early 50s) by the end of follow-up, so they had not reached the age range when breast cancer diagnoses are most common.