Drugs used to treat female infertility do not appear to be associated with an increased risk of breast cancer, according to a new report.

Based on these findings and others, “infertile women should not worry about breast cancer,” Dr. Allan Jensen from the Danish Cancer Society, Copenhagen, told Reuters Health.

Jensen and his associates evaluated the effects of different types of fertility drugs on the risk of breast cancer, after taking account of reproductive factors that are known to affect the risk, in a study involving more than 54,000 women with infertility problems.

Out of that whole group, 331 women developed breast cancer after an average of 14 years, the investigators report in the journal Cancer Epidemiology, Biomarkers, and Prevention.

After adjustment, the researchers found that clomiphene and four synthetic hormones used to boost fertility did not significantly affect the risk of breast cancer.

The use of progesterone was associated with an increased risk of subsequent breast cancer, the investigators say, but this increased risk was based on only eight cases.

“The progesterone results are limited by a low number of cases,” Jensen said. “We will therefore increase the follow-up period in order to collect more cases. Also, as progesterone is mainly used for IVF patients, we will go into more details with this subgroup.”

In any case, he added, “we are talking about small increased relative risks, and therefore the absolute risk will still be low.”

SOURCE: Cancer Epidemiology, Biomarkers, and Prevention, July 2007.