(Reuters Health) - Assisted reproductive technologies don’t carry an overall increased risk of breast, ovarian or uterine cancer, according to a new study in the UK.

Although women who undergo fertility treatments do face a small increased risk of noninvasive breast cancer and ovarian tumors, it’s more likely due to other predisposing factors, the study authors wrote in the medical journal BMJ.

“Hormones in the reproductive cycle contain cell growth controls, and there are multiple examples of situations where other hormonal therapies have resulted in unexpected increased risks of cancer,” said senior study author Dr. Alastair Sutcliffe of the University College London’s Great Ormond Street Institute of Child Health.

“It’s not unreasonable to consider if the exposure to reproductive hormones might, in rare cases, be associated with a downstream effect on cancer in the longer term,” Sutcliffe told Reuters Health by email.

Sutcliffe and colleagues analyzed data collected over an average of nearly nine years from nearly 256,000 women had assisted reproduction between 1991 and 2010, including 3155 who later developed ovarian, breast or uterine cancer.

When the researchers compared these women to a similar group of women who had not received fertility treatments, they found there wasn’t much of a difference for risk of uterine cancer or invasive breast cancer.

Noninvasive breast cancer and ovarian tumors did increase slightly among those who had fertility treatments. For breast cancer, the slight increase in risk was associated with a higher number of treatment cycles. For ovarian cancer, the increased risk was limited to women who had endometriosis, female-factor infertility such as tubal disease, or an ovary disorder.

“We were surprised a little by the increased risk of ductal breast cancer, although we can explain it by increased health surveillance of these intensively medicalized couples rather than a true effect,” Sutcliffe said, particularly since invasive cancer rates were the same in both groups.

A limitation of the study is that it compares women who received fertility treatments to the overall population, rather than other women with infertility issues who decided not to receive treatment. However, this type of study likely wouldn’t have enough participants and is often tough to replicate, said Dr. Paul Hardiman of Whittington Hospital in London. Hardiman, who wasn’t involved with this study, researches the risks of endometrial, ovarian and breast cancer in women with polycystic ovary syndrome.

“People may latch onto a message here about the risks of cancer, but I read this as a positive,” he told Reuters Health by phone. “Fertility treatments have little or no effect, and women shouldn’t be scared. They should take comfort in this.”

Previous studies have shown that women who have fewer children or have their first child later in life are more likely to develop a reproductive organ cancer, so other medical characteristics likely explain the risk increase rather than the fertility treatments, Hardiman said. Researchers still want to know why women with infertility are more likely to develop certain cancers and how other factors such as socioeconomic status, breastfeeding practices, and oral contraceptive use could affect cancer risk.

“We need to rule out the underlying predispositions,” Hardiman said. “We should also look at common drugs given to induce ovulation that may carry an increased risk for cancer.”

Sutcliffe and colleagues will repeat the study in coming years, too, to understand how cancer risks related to fertility treatments develop over time as women age.

“Women seeking fertility treatments should know the benefits and risks for themselves and their baby, even if they want a baby at all costs,” Hardiman said. “The unnaturally high levels of estrogen in some treatments may worry some women, but this study should reassure them.”

SOURCE: here BMJ, online July 11, 2018.