Among women who received clomiphene, the analysis showed no overall, significantly increased risk of any cancer. But when the analysis broke out the incidence of these three cancer types individually, it showed that the subgroup of women who were nulligravid at treatment and remained nulligravid throughout follow-up had a significant, 3.6-fold increased risk of ovarian cancer, compared with women who did not receive clomiphene. But Dr. Scoccia cautioned that only 13 women were in this subgroup.
A second subgroup analysis that looked specifically at the 31 women who developed invasive breast cancer showed that women who received clomiphene during 12 or more ovulatory cycles had a 69% higher rate of invasive breast cancer than did those who never received clomiphene.
Dr. Scoccia also found that none of the analyses of women who had received a gonadotropin showed any subgroup with an increased rate of cancer.
"Overall, these findings are reassuring," he said, but cautioned that because the women averaged 30 years of age at the time they received fertility treatment, even after 30 years of follow-up these women generally remained younger than the peak age for incidence of these cancer types; hence, further follow-up of the cohort will help further define whether they face increased lifetime cancer rates. He also noted that the higher cancer rates seen with increased clomiphene treatment may link to more resistant infertility among these women rather to than the clomiphene they received, but added "we don’t think it is explained by more resistant infertility alone."
Dr. Hargreave and Dr. Scoccia had no disclosures.
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