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 say the results showed there was a need for further research, although they stressed the apparent risks were still very low.

China Daily-Reuters-AFP