Major Study Finds IVF Not Linked to Cancer Risk, But There's a Catch

Since fertility treatments such as in vitro fertilisation (IVF) began, there has been concern they could cause cancer.

Concerns have included whether aspects of treatment – such as taking hormonal medications, or puncturing the ovaries to retrieve eggs – could stimulate the growth of cancer cells.

Now, our new study, published on Wednesday, has found women who underwent fertility treatments had a comparable overall rate of cancer to similarly aged women.

However, there were some differences: they had more uterine, ovarian, and melanoma cancers, and fewer lung and cervical cancers. Let's take a look at what this means.

What we did

Our study wanted to find out whether women who underwent fertility treatments had a different rate of cancer from the general population.

We used individual records from Medicare and the Pharmaceutical Benefits Scheme to find women who had fertility treatments between 1991 and 2018. We linked this data to the Australian Cancer Database to find cancer diagnoses.

We found 417,984 women who received fertility treatments and followed them for about a decade on average:

• 274,676 women had treatments where the egg was removed from the women's body (IVF and similar treatments)
• 120,739 women had treatments with a specialist where the egg was not removed (mainly intrauterine insemination)
• 175,510 women received a prescription for clomiphene citrate (also known as Clomid), a medication that induces ovulation.

One woman could have had multiple types of treatment.

Their median age (the midpoint of their ages) was 32–34 years. Compared to the general population, fewer lived in disadvantaged areas.

Overall, the findings are reassuring for women who have received or are planning fertility treatments (FatCamera/Canva)

We compared these women's rates of cancers to women in the general population, by statistically matching them on factors such as age and the state they lived in.

What we found

Women who received fertility treatments, either with or without egg removal, had close to the exact total number of cancers we would expect in the general population of women.

But women who used clomiphene citrate had 1.04 times the rate of cancer, or 8.6 extra cancers for every 100,000 women treated each year.

Rates of uterine cancer, ovarian cancer (except for those who used clomiphene citrate), and melanoma were 1.07–1.83 times higher, depending on treatment type. This means about three to seven more of these cancers for every 100,000 women treated each year.

This difference could be due to risk factors unrelated to the treatment. For example, endometriosis – a risk factor for infertility – is linked to ovarian cancer. Similarly, more Caucasian women receive fertility treatments, and fair skin is an established risk factor for melanoma.

Across all treatments rates of cervical cancer and lung cancer were 1.43–1.92 times lower. This translates to around two to six fewer cancers for every 100,000 treated women each year.

These decreases could be due to women receiving fertility treatment being less likely to smoke. Women who receive fertility treatment may also be more likely to be screened for cervical cancer, as clinicians often encourage them to get screened before treatment. But this is anecdotal – we don't yet have data on this.

What this means

Overall, these findings are reassuring for women who have received or are planning fertility treatments.

The number of people undergoing fertility treatments is increasing worldwide. These findings deepen our understanding of the types of cancers diagnosed in women who receive fertility treatment.

Our study shows some cancers are more common in women who received fertility treatments than in the general population of women.

However, the absolute numbers of these cancers are small, similar to those observed for women using some other medical interventions (including the contraceptive pill).

It is normal to see differences in cancer risk in specific populations when compared to the general population.

So, does this mean IVF does not cause cancer?

This study design cannot determine if fertility treatments themselves cause or prevent cancer.

Though fertility treatments may contribute to cancer risk, women who receive fertility treatments have a different health and socio-demographic profile to the general population of women. These factors may affect cancer risk.

We did not have any data on why women were using fertility treatments to get pregnant and whether this is connected to their cancer risk. For example, we don't know if they were receiving treatment for medical infertility, or for another reason (such as same-sex couples trying to conceive).

Our study also only followed women for around ten years, and the cancer risk profile may change as these women age.

The takeaway

As with every medical treatment, it is important for women and their healthcare practitioners to make informed decisions before and after fertility treatment, including considering potential changes in cancer risk.

Women considering fertility treatment, and those who've used fertility treatment, should continue to participate in the routine cancer screening programs they're eligible for.

Related: Popular Anti-Aging Supplement May Fuel Cancer Growth – Here's Why

If women are worried about their risk of cancer, they should consult their doctor to understand the steps they can take to reduce their risk.

Adrian Raymond Walker, Research Fellow, Centre for Big Data Research in Health, UNSW Sydney and Claire Vajdic, Professor, Health and Medicine, UNSW Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.