Do Fertility Drugs Increase Your Risk of Getting Cancer?

Do fertility drugs cause cancer? What about IVF treatment? It is true that a few studies seemed to find a connection between fertility drug use and an increased risk of breast or uterine cancer, specifically with the drug Clomid. 

All medications, including fertility drugs, come with risks. But should you be concerned about an increased cancer risk? Let's take a look.

Fertility Drugs and Cancer Risk

In 2005, a widely publicized study reported that Clomid use might increase the risk of uterine cancer. However, since that time, more studies have been done, and most have found no significant increase in cancer risk after Clomid use.

In fact, a 2019 review—which concluded that there is "no definitive relationship between the use of fertility drugs and cancer"—found that because estrogen helps protect against colorectal cancer, the risk of cancer should decrease in women who use fertility drugs.

The problem with many of these studies is they don't take into account other potential risk factors for uterine cancer. Namely, if a woman never experiences pregnancy, her risk of cancer increases. Also, obesity is not only a risk factor for infertility, but it is also a risk factor for cancer.

It may not have been the fertility drugs at all. Instead, the increased incidence may be attributed to the reason behind infertility itself or any number of other factors not taken into account in this study. Many studies have found a possible connection between certain causes of infertility—such as diet or obesity—and an increased risk of cancer. Another common problem with these studies is the sample sizes were too small.

Ovarian Cancer Risk

The strongest evidence that Clomid and other ovarian-stimulating drugs do not increase the risk of ovarian cancer comes from a Cochrane Review. The review included studies from 1990 through February 2013. The studies compiled together included 182,972 women.

Seven of the studies found no evidence of increased ovarian cancer in women who use any fertility drug (including Clomid) when comparing their risk to other women with fertility problems who did not use fertility drugs.

According to the review, studies that did find increased cancer risk were not reliable because they failed to take into consideration the risk of infertility itself or the sample size was too small to draw conclusions.

Borderline Ovarian Tumors and IVF

The Cochrane review did find a possible increased risk of borderline ovarian tumors in women who went through IVF treatment. This risk was not present after Clomid or Clomid with gonadotropins treatment alone. The treatment of borderline ovarian tumors isn’t as intense and involved as with typical ovarian tumors, and the prognosis for women with a borderline tumor is very good.

A 2015 study tried to further investigate the possible risk of borderline ovarian tumors and fertility treatment. What they found was that there was no strong link between borderline ovarian tumors and fertility drug use.

Researchers found that the risk of borderline ovarian tumors was higher for women who used progesterone compared to those who never did and higher in women who had four or more cycles of progesterone supplementation.

That said, the number of women in the study with borderline tumors was small. Follow-up studies with larger groups of women are needed.

Endometrial Cancer Risk

Could fertility drugs increase the risk of endometrial cancer? A Cochrane Review of 19 studies concluded that due to poor study design, it’s not possible to say with any certainty whether endometrial cancer risk increases after exposure to fertility drugs.

There did seem to be a possible increased risk in women who had very high doses of Clomid (greater than 2,000 mg—the average starting dose is only 50 mg) and took Clomid for seven or more cycles.

However, the current research wasn’t able to distinguish whether that increased risk was due to Clomid or underlying fertility factors. For example, PCOS is known to increase the risk of developing endometrial cancer. 

Long-Term Risk of Breast Cancer After IVF

Could IVF (in vitro fertilization) treatment increase your risk of breast cancer? The current research says not likely.

One of the largest studies to date included 25,108 women, with an average follow-up of 21 years after treatment. These were women from the Netherlands, who received IVF treatment between 1980 and 1995. There was no increased risk of breast cancer in women who received IVF compared to those who received non-IVF fertility treatments.

Interestingly, researchers found the risk of breast cancer was lower for women who had seven or more IVF cycles compared to women who had one or two cycles. It’s unclear why this is.

IVF and Ovarian Cancer

A 2018 study analyzed the cancer risk in women who had gone through IVF treatment, including over 250,000 British women and spanning treatment cycles between 1991 and 2010. The good news was that they found no increased risk of breast or uterine cancer in the former IVF patients. The bad news is that they found an increased risk of ovarian cancer.

Like in the studies mentioned above, the consensus is that the increased risk isn't caused by IVF treatment itself but the fact that the women needed treatment. Infertility and the need for IVF are suspected as the risk, not the fertility drugs used during treatment

With that said, the study also found that the cancer risk was higher in the first three years after treatment. So, it's not possible to completely rule out that fertility drugs played a role in the cancer risk. Close monitoring in the years after IVF treatment may be smart.

A Word From Verywell

The consensus is that fertility drugs do not increase your risk of developing breast or uterine cancer. Also, some studies have looked at fertility drug use and other kinds of cancers (thyroid and skin cancers, for example), and they have also found no significant increase in risk.

However, because infertility itself is a risk factor for cancer, follow-up after diagnosis is recommended. Women with primary infertility, who never become pregnant and give birth, as well as women diagnosed with endometriosis, may particularly have an increased risk of developing cancer. 

PCOS, a common cause of infertility, is also known to come with an increased risk of developing endometrial cancer. It's possible that very high doses of Clomid, or treatment that extends beyond seven cycles, may increase the risk of endometrial cancer. But the current evidence can't distinguish whether this increased risk comes from Clomid or infertility itself.

Also, it's important to keep in mind that the technology of fertility treatment is changing. Lower doses of drugs are now being used than in the early days of treatment, and many of the studies on cancer and fertility treatment include women treated in the 1980s, more aggressively than they might be today.

Studies on cancer and fertility treatment also require long-term follow-up. It may be decades before we can really say what impact fertility treatment at age 35 will have on a woman who is 65 or 70 years old. While more research must be done, for now, fertility drugs are (mostly) off the hook.