June 15, 2004 -- Taking fertility drugs does not appear to increase a woman's risk of developing ovarian cancer, a new study from the National Cancer Institute suggests.
Researchers found no associations between the use of medications that stimulate ovulation and ovarian cancer in a study involving more than 12,000 women who had trouble conceiving. However, a slight increase in risk was seen among women followed for the longest time, but researchers say this increase may not be related to the use of fertility drugs.
"In general our findings are very reassuring," lead researcher Louise Brinton, PhD, tells WebMD. "We failed to confirm a major increase with the use of these drugs, but most of these women are still relatively young. For this reason, the association warrants further follow-up."
Early Findings Mixed
Since their introduction almost four decades ago, ovulation-stimulating drugs like Clomid have been prescribed to millions of infertile women. Previous studies assessing the impact of these drugs on ovarian cancer risk have been mixed, with one study suggesting up to a 27-fold increase in cancer risk among treated women who never got pregnant and other studies failing to find any link at all.
The NCI trial included 12,193 women who were seen at five infertility clinics throughout the country between 1965 and 1988. Of these, more than 4,000 women had used a fertility drug.
By 1999, 45 of the women had been diagnosed with ovarian cancer, which was almost twice the number expected in the general population.
But when the researchers adjusted for other ovarian cancer risk factors, the use of fertility drugs was not found to significantly increase cancer risk.
In other words, ovarian cancer risks were similar regardless of whether these women used fertility drugs or not.
Clomid users actually had slightly fewer ovarian cancers than would be expected in the general population, while users of the protein hormone gonadotropin had slightly more cancers.
Fifteen years after treatment, the odds of developing ovarian cancer more than doubled among the small group of gonadotropin users followed for many years.
"These women are only now beginning to reach the age range where ovarian cancer is most often diagnosed," Brinton says. "That is why it is important to continue following them."
Women Who Don't Get Pregnant
Fertility expert Alan DeCherney, MD, says recent studies are consistent in finding no link between fertility drug use and ovarian cancer risk. It is now clear that women who never achieve a pregnancy are at increased risk, however, and DeCherney says earlier studies failed to take this into consideration.
"We now know that women who fail to get pregnant -- with or without fertility treatments -- are at greater risk," says DeCherney, who is a professor of obstetrics and gynecology at UCLA School of Medicine and a past president of the American Society for Reproductive Medicine. "Since those who can't conceive are the ones who take fertility drugs, it is easy to see why the early studies made this association."