Breast cancer risk greatly increased by hormone replacement therapy

How does hormone replacement therapy affect the risk of breast cancer?

The risk of developing breast cancer by using hormone replacement therapy is twice as high as previously thought. A new extensive study confirms that hormone replacement therapy can be the direct cause of cancer.

In the current study by the Collaborative Group on Hormonal Factors in Breast Cancer, it has now been found that the risk of breast cancer is massively increased by hormone replacement therapy. The results of the study were published in the English language journal "The Lancet".

Is hormone replacement therapy dangerous for women?

The longer women take hormone replacement therapy, the higher the risk of developing breast cancer. And it was also shown that the increased risk does not disappear if the women stop treatment, the researchers report. Women who are on hormone replacement therapy or have previously used such treatment should therefore pay more attention to signs of breast cancer. There is no reason to panic, but women who are affected should have a medical breast examination done if they are unsure.

Risk twice as much as was actually assumed

The risk of breast cancer from hormone replacement therapy is twice as high as previously thought, because it can last up to ten years or more after women have stopped taking hormone replacement therapy. The research team reports that one in 50 women of average weight who have taken the most common form of hormone replacement therapy (combined daily use of estrogen and progestogen) over a period of five years has breast cancer.

No risk from hormone replacement therapy in the first year?

Women should be aware of the risk so that this can be considered when considering hormone replacement therapy. Menopause can have uncomfortable side effects, and hormone replacement therapy products can help relieve symptoms. But no medication is completely risk-free and it is important that women can make an informed decision based on the individual benefits and risks. According to the current results, women should only take hormone replacement therapy in the lowest dose and for the shortest possible time. The study also shows that there may not be an increased risk in the first year.

Should policies be updated?

Hormone replacement therapy has long been associated with breast cancer, and to a lesser extent with ovarian cancer. However, the issue has been controversial. Many general practitioners have long argued that hormone replacement therapy is no cause for concern. Such statements should be reconsidered given the new results. Existing guidelines on the use of hormone replacement therapy should also be updated if necessary.

How much was the risk increased?

Hormone replacement therapy appears to be the cause of about five percent of breast cancers. The risk of cancer increases with the time women take hormones, and the types of cancer are usually estrogen receptor positive, meaning that they are controlled by estrogen. In western countries, 6.3 percent of women of normal weight over the age of 50 without breast cancer will develop breast cancer within the next 20 years. For women who took the most common hormonal combination, the current study saw an increase to 8.3 percent. If the women only took progestins temporarily (about ten to 14 days a month), the risk was 7.7 percent. However, if only estrogen was used because no progestin is needed, the risk was 6.8 percent. Obese women generally have an increased risk of breast cancer because their adipose tissue produces additional estrogen after the menopause. The study found that hormone replacement therapy did not further increase this risk. (as)

Author and source information

This text corresponds to the requirements of the medical literature, medical guidelines and current studies and has been checked by medical doctors.


  • Collaborative Group on Hormonal Factors in Breast Cancer: Type and timing of menopausal hormone therapy and breast cancer risk: individual participant meta-analysis of the worldwide epidemiological evidence, in The Lancet (query: 30.08.2019), The Lancet

Video: Study: Post-Menopausal Hormone Therapy Increases Cancer Risk (January 2022).