‘Breast cancer drug tamoxifen ups endometrial cancer risk in premenopausal women’

Tamoxifen, a widely used treatment for breast cancer, increased the risk of various uterine diseases including endometrial cancer in premenopausal women with breast cancer, a study showed. 

The research team, led by Professors Park Hyun-tae and Ryu Ki-jin at the Department of Obstetrics and Gynecology, Korea University Anam Hospital, published their study in JAMA Network Open recently. The study is titled, “Risk of Endometrial Polyps, Hyperplasia, Carcinoma, and Uterine Cancer After Tamoxifen Treatment in Premenopausal Women With Breast Cancer.”

Tamoxifen is most commonly taken by breast cancer patients to prevent a recurrence. The drug is usually taken for a long time ranging from five to 10 years. 

Postmenopausal women are known to have an increased risk of endometrial cancer if they take tamoxifen, so regular screening is necessary.

However, it has been unclear whether tamoxifen increases the risk of endometrial cancer in premenopausal women due to a lack of research, although breast cancer patients in the premenopausal stage commonly take tamoxifen as a first-line therapy.

The research team analyzed the 18-year (between 2002 and 2019) data of 78,320 Korean breast cancer patients aged between 20 and 50, using the database of the National Health Insurance Service (NHIS), a single medical insurer in Korea. 

The researchers found that the premenopausal tamoxifen group had a 3.8 times higher incidence of endometrial cancer compared to the premenopausal control group who did not take tamoxifen. The incidences of other uterine cancer, endometrial polyps, and endometrial hyperplasia were also significantly higher by 2.3 times, 3.9 times, and 5.6 times, respectively, compared to the control group. 

By annual incidence, 20 per 1,000 tamoxifen takers developed endometrial polyps, 13.5, endometrial hyperplasia, and 2, endometrial cancer. 

The incidence of endometrial cancer was similar to the incidence of that disease among Western postmenopausal breast cancer patients, which was 1.83 per 1,000. 

The study was the first to identify the increased incidence of endometrial cancer among tamoxifen-taking premenopausal breast cancer patients based on a large-scale population analysis.  

In particular, the study is meaningful in that it presented important data on the increase in various cervical diseases associated with tamoxifen intake in Korean women, who have a higher incidence of breast cancer at a younger age than Western women, the research team said. 

The research team noted that many guidelines do not specify warnings about the risk of uterine disease or offer a guide for premenopausal women taking tamoxifen.

“We hope that the results of this study will serve as an opportunity to improve the treatment process and guidelines for the prevention and management of tamoxifen-related uterine diseases, especially for Korean women,” the research team said.