News release

From: The University of New South Wales

Women who used fertility treatments had no higher overall risk of invasive cancer than other women, a large Australian study led by researchers from UNSW Sydney has found.

The study, published today in JAMA Network Open, analysed health records of more than 417,000 women and found some specific cancers were slightly more common, while others were less common.

The researchers say the findings need to be interpreted with caution, and in the context of the many factors that influence cancer risk.

Joint-lead author Dr Adrian Walker, from UNSW’s Centre for Big Data Research in Health, said the overall findings were reassuring – women who receive fertility treatment do not have a higher total incidence of cancer than other women.

“Women who’ve had assisted fertility should continue to participate in routine cancer screening programs they’re eligible for,” he said. “And they should discuss their cancer risk with their doctor, to understand how else they can reduce their risk.”

Some cancers higher, others lower

The study analysed national health and cancer records from 417,984 Australian women who underwent medically assisted reproduction between 1991 and 2018. This included IVF, intrauterine insemination and treatment with the fertility drug clomiphene. The study examined cancer outcomes in these women over an average of 10 years.

The researchers compared how often cancer occurred in these women with how often it occurred in Australian women of the same age and in the same calendar years.

Uterine and ovarian cancer were slightly more common, as was melanoma. A non-invasive form of breast cancer was also more common in women who had IVF, but invasive breast cancer was not increased.

At the same time, some cancers – including cervical and lung cancer – were less common.

“It is very normal for a specific group of people to have a slightly different cancer profile from the general population”, said Dr Walker.

“But as we see here, that doesn’t mean that their overall risk is increased.”

Study lead Professor Claire Vajdic, from UNSW‘s Kirby Institute said the findings need to be interpreted carefully.

“This study focused on comparing rates of cancer in different populations, not whether fertility treatments themselves cause cancer. As such, we must consider the pre-existing risks of cancer in these populations when interpreting the findings,” she said.

“Women with infertility who are having or have had treatment, like all women, should ensure that they have regular check-ups, and seek further evaluation if they have concerns about unusual symptoms.”

Relative risk versus absolute risk

Of the cancers that occurred at a higher rate than in general population, uterine cancer was between 23% and 83% more common, depending on the type of fertility treatment. Ovarian cancer was around 18% to 23% more common in women who had IVF or related treatments, while melanoma was about 7% to 15% more common.

On the other hand, some cancers were less common. Cervical cancer rates were about 40% lower than in the general population, and lung cancer rates were about 30% lower.

However, when the researchers looked at the actual number of additional cases, the difference was small. Across the cancers that were more common, the largest increase amounted to three to seven extra cases per 100,000 women per year.

So even where a relative increase was observed, the overall chance of developing cancer remained low.

“Very few medical treatments are without risk, but the elevated cancer incidence here is low,” Prof. Vajdic said.

Many factors to consider

The researchers say there could be many reasons why certain cancers were more common in women who had fertility treatment.

“Women who need fertility treatment may differ from other women in ways that affect cancer risk,” Prof. Vajdic said.

“Certain underlying causes of infertility, such as endometriosis and polycystic ovary syndrome, are known to increase the risk of uterine and ovarian cancers.”

The researchers showed Australian women who underwent fertility treatment were more likely to live in major cities and be socioeconomically advantaged. Although not examined in this study, women having fertility treatment are also more likely to have fair skin and be less likely to smoke. Additionally, before starting fertility treatment, doctors must check that women are up to date with any recommended routine cancer screening.

All these factors will contribute to the cancer patterns observed in this study, including reduced lung cancer rates and reduced cervical cancer rates.

“What this study does is describe cancer patterns we’re seeing at a population level,” Dr Walker said.

“It doesn’t tell us the risk of receiving treatment, or the risk for individual women who undergo treatment."

Looking ahead

Because many women in the study were still relatively young at the end of follow-up, the researchers said longer follow-up would provide additional insights.

“Continued cancer awareness is important as this population ages,” Prof. Vajdic said.

The researchers concluded that cancer risk after fertility treatment was not higher overall, and further research to better understand differences in incidence for individual cancers will help women and their doctors make informed decisions.