Women given drugs during fertility treatment to stimulate their ovaries to produce extra eggs have an increased risk of developing borderline ovarian tumors, Dutch researchers said on Thursday.
A large 15-year study found women undergoing in-vitro fertilization (IVF) were twice as likely to develop ovarian malignancies, defined as either cancer or borderline tumors, as similarly sub-fertile women who were not treated.
The risk was concentrated in borderline tumors, which have abnormal cells that may become cancerous but usually do not. The danger of invasive ovarian cancer was slightly higher in the IVF treatment group but this was not statistically significant.
Fertility experts said the results showed there was a need for further research, although they stressed the apparent risks were still very low.
"This ... goes some way to answering the questions that so many IVF patients ask. However, the results should be kept in proportion as the increase shown was from around five in a thousand to seven per thousand women," said Peter Braude of Kings College London.
Braude, who was not involved in the Dutch study, said the possible risks needed to be balanced against the important objective of IVF in conceiving a child.
Lead researcher Flora van Leeuwen of the Netherlands Cancer Institute in Amsterdam said the findings were significant because the study was the first to include a comparison group of sub-fertile women not undergoing IVF.
That is important because having difficulty conceiving or never having been pregnant are in themselves known risk factors for ovarian tumors.
The study observed 25,000 women, of whom 19,000 received IVF. It found 61 ovarian malignancies among the IVF group, of which 31 were borderline tumors and 30 invasive cancer, a proportion of borderline cases that was unusually high.
Richard Kennedy, general secretary of the International Federation of Fertility Societies (IF), noted that other studies over the past decade looking at ovarian stimulation and cancer risk had been generally reassuring.
"The IF 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," he said in a statement.
The results of Dutch study were published in the journal Human Reproduction.