A New Study Finds Breast Cancer Risk from Hormone Replacement Therapy is Much Higher Than Previously Thought

For years, medical researchers have assured patients that hormone replacement therapy—a common treatment to alleviate symptoms of menopause—triggers just a slightly elevated risk of breast cancer in participants. But according to a new study published in the Lancet, the risk of developing breast cancer for those on HRT is twice as high as researchers previously thought, with the likelihood being as high as one in 50 that someone who is on the most common form of HRT for five years will develop breast cancer. The study also found that in some cases, the higher risk continues for much longer after HRT has ended than researchers once assumed.

More on the study, which analyzed dozens of previously published studies on the effects of HRT, from the Guardian:

It finds that the longer women take it, the greater their risk, with the possibility that just one year is risk-free. It also finds that the risk does not go away as soon as women stop taking it, as had been previously assumed.

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The research, published in the Lancet medical journal, says one in 50 women of average weight taking the most common form – combined daily oestrogen and progestogen – for five years will get breast cancer as a result.

That risk is twice what was thought, because it continues at some level for 10 or more years after women stop taking HRT. There are about 1 million women in the UK on HRT, 5 million in the rest of Europe and 6 million in the US.

According to CNN, the study found that “every type of hormone replacement therapy, except for vaginal estrogens, was associated with excess breast cancer risks:”

The researchers found that for women of average weight in Western countries, five years of using estrogen plus a daily progestogen hormone therapy, starting at age 50, was associated with an increased risk of breast cancer up to age 70.

Specifically, the research suggests that the estimated incidence of breast cancer at ages 50 to 69 was tied to an increased risk — from 6.3% of women who never used hormone replacement therapy to 8.3% of those who used the therapy daily for five years.

That’s an increase of about one extra cancer case in every 50 users of the therapy, according to the research.

And there is elevated risk for those on other forms of HRT as well. Again, per CNN:

Similarly, five years of using estrogen plus intermittent progestogen hormone therapy was tied to an increased risk, from 6.3% to 7.7%, representing an increase of one extra cancer case in every 70 users of the therapy, the research suggests.

The research also suggests that five years of using an estrogen-only therapy was tied to an increased risk, from 6.3% to 6.8%, which would be an increase of one extra cancer case in every 200 users of the therapy.

If you’re on HRT or have been, should you worry? According to Dr. Janice Rymer, a gynecologist and the vice president of the Royal College of Obstetricians and Gynaecologists in the United Kingdom, it’s best to speak with your doctor to weigh the risks.

“Women must be informed of the small increase in risk of breast cancer so they can weigh these up against the benefits that they may have from taking HRT,” Rymer said in a statement. “These findings should not put women off taking HRT if the benefits—such as protection of bones and decrease in cardiovascular risk—outweigh the risks,” she continued.