Women who have to take fertility drugs in an attempt to get pregnant do not have an increased risk of developing breast cancer, a new study indicates.

According to US researchers, women should be reassured by these findings.

They looked at almost 10,000 women who had been assessed for infertility between 1965 and 1988. Among these, almost 800 developed breast cancer. The women were followed up over a 30-year period.

The study focused specifically on clomiphene citrate, better known as Clomid, and gonadotropins, both of which help stimulate ovulation.

"We wanted to evaluate the long-term relationship of fertility medications and breast cancer risk after controlling for other factors that have been shown to be correlated with both breast cancer risk and use of those drugs. Overall, our data show that use of fertility drugs does not increase breast cancer risk in this population of women, which is reassuring," said Dr Louise Brinton of the National Cancer Institute in Maryland.

The researchers did find an increased risk of invasive breast cancer in a small number of women, however they had used Clomid at least 12 times in an attempt to get pregnant. Patients rarely exceed six cycles of the drug.

"Given the high doses of drugs received (overall) by our study participants and the lack of large increases in breast cancer risk many years after exposure, women previously exposed to such drugs should be reassured by these findings," Dr Brinton insisted.

She called for more research into the potential effects of other fertility drugs, such as ones given during IVF, on breast cancer rates.

Details of these findings are published in the journal, Cancer Epidemiology, Biomarkers & Prevention.