(HealthDay News) — Women with ever use of clomiphene have no increased breast cancer risk, although women undergoing multiple clomiphene cycles have an increased risk of invasive breast cancer, according to a study published online April 3 in Cancer Epidemiology, Biomarkers & Prevention.
Louise A. Brinton, PhD, MPH, from the National Cancer Institute in Rockville, MD, and colleagues conducted extended follow-up in a cohort of 12,193 women evaluated for infertility between 1965 and 1988. A total of 9,892 women were followed through 2010 via passive and active (questionnaire) means to examine the impact of fertility drugs on breast cancer risk.
RELATED: Breast Cancer Resource Center
The researchers observed 749 breast cancers during 30.0 median years of follow-up (285,332 person-years).
Breast cancer risk was not associated with ever use of clomiphene citrate (among 38.1% of patients; hazard ratio [HR], 1.05; 95% confidence interval [CI], 0.90 to 1.22). Patients who received multiple cycles had somewhat higher risks, with a significant elevation in the risk of medical record-confirmed invasive cancers (HR, 1.69; 95% CI, 1.17 to 2.46). After adjustment for causes of infertility and multiple breast cancer predictors, the risk remained relatively unchanged.
An inconsistent correlation with risk was seen for use of gonadotropins (used by 9.6% of patients, mainly in conjunction with clomiphene). For women who remained nulligravid, the correlation of use with invasive cancers was significantly increased (HR, 1.98; 95 percent CI, 1.04 to 3.60).
“Given our focus on a relatively young population, additional evaluation of long-term fertility drug effects on breast cancer is warranted,” the researchers wrote.
One researcher disclosed financial ties to the pharmaceutical industry.