THURSDAY, Oct. 27 (HealthDay News) -- Women who undergo ovarian stimulation to produce extra eggs for in-vitro fertilization (IVF) are at increased risk for a type of growth known as "borderline ovarian tumors," new research suggests.

Borderline ovarian tumors are typically not aggressive, according to the U.S. National Cancer Institute. Even if the tumor does spread, the vast majority of women survive borderline ovarian tumors.

Even so, treating borderline ovarian tumors can require extensive surgery, explained lead researcher Flora van Leeuwen, head of the epidemiology department in The Netherlands Cancer Institute.

For the study, researchers examined data from over 19,000 infertile women in the Netherlands who underwent ovarian stimulation prior to IVF and about 6,000 infertile women who did not undergo IVF.

After 15 years of follow-up, the women who underwent ovarian stimulation were four times more likely to develop a borderline ovarian tumor, according to the findings published in the Oct. 27 online edition of the journal Human Reproduction.

"Our data clearly show that ovarian stimulation for IVF is associated with an increased risk of borderline ovarian tumors and this risk remains elevated up to more than 15 years after the first cycle of treatment," van Leeuwen explained in a journal news release.

Overall, however, the number of women developing any sort of ovarian tumor was low. The cumulative risk in the general population of an ovarian malignancy for women under age 55 in the Netherlands is 0.45 percent. For women who undergo IVF, it's 0.71 percent, "with the increase being due to borderline tumors of the ovary," van Leeuwen added.

The low number of women in the study who developed ovarian malignancies prevented the researchers from determining if repeated IVF cycles increased the risk of ovarian malignancies. They noted in the news release that they are expanding their study population to examine that issue.

"If we find out that women who receive several IVF cycles or large doses of ovarian-stimulating drugs are at a greater risk of ovarian cancer, then these women would need to be informed about these risks when continuing IVF treatment and possibly advised to discontinue treatment after three to six cycles (depending on which number of cycles would be associated with the high risk of ovarian malignancies)," van Leeuwen noted.

The International Federation of Fertility Societies (IFFS) issued a statement in response to the new study findings. In it, general secretary of the IFFS, Richard Kennedy of Coventry, England, said: "Over the last decade, several reports have considered the long-term risks of ovarian stimulation practiced as part of the IVF process. These reports have been generally reassuring in terms of risk of ovarian cancer."

However, Kennedy added, "This new research has highlighted the presence of an increased risk of borderline tumors . . . and has once again posed a question about the long-term risks of ovarian stimulation further confounded by the known underlying risks for these patients. The IFFS remains of the view that the long-term risks are low but calls for continued vigilance through reporting of long-term outcomes with international collaboration."

More information

The American Cancer Society has more about ovarian cancer.