AUTHOR=Choi Soojeong , Lee Young Jae , Jeong Jae Ho , Jung Jinhong , Lee Jong Won , Kim Hee Jeong , Ko Beom Seok , Son Byung Ho , Ahn Sei Hyun , Lee Yura , Chung Il Yong 

TITLE=Risk of Endometrial Cancer and Frequencies of Invasive Endometrial Procedures in Young Breast Cancer Survivors Treated With Tamoxifen: A Nationwide Study

JOURNAL=Frontiers in Oncology

VOLUME=Volume 11 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2021.636378

DOI=10.3389/fonc.2021.636378

ISSN=2234-943X

ABSTRACT=Background: Although the guidelines recommend gynecological assessment and close monitoring for symptoms of endometrial cancer in postmenopausal breast cancer survivors taking tamoxifen (TAM), the risk of endometrial cancer in young breast cancer survivors has not yet been fully assessed. This study aimed to investigate the risk of developing endometrial cancer and the frequencies of gynecological examinations in young breast cancer survivors taking TAM in South Korea. 
Methods: A nationwide retrospective cohort study was conducted using the Health Insurance Review and Assessment Service claims data. Kaplan–Meier analysis and the log-rank test were used to assess the probability of endometrial cancer, benign endometrial conditions, and the probability of invasive endometrial procedure. To analyze the risk of endometrial cancer and benign endometrial conditions, we used a multivariable Cox proportional hazards regression model.
Results: Between 2010 and 2015, 60,545 newly diagnosed female breast cancer survivors were included. The total person-years were 256,099 and 140 (0.23%) patients developed endometrial cancer during the study period. In breast cancer survivors aged ≥60 years (hazard ratio [HR], 5.037; 95% confidence interval [CI], 2.185–11.613), 50–59 years (HR, 4.34; 95% CI, 2.122–8.891), and 40-49 years (HR, 2.121; 95% CI, 1.068–4.213), TAM was associated with an increased risk of endometrial cancer. In subjects aged below 40 years, TAM did not significantly increase the risk of endometrial cancer (HR, 2.048; 95% CI 0.658-6.377). However, among the TAM subgroups, symptomatic breast cancer survivors aged below 40 years (HR, 12.460; 95% CI, 2.698–57.522) and aged 40-49 years (HR, 9.667; 95% CI, 4.966–18.819) showed significantly increased risks of endometrial cancer. Among the TAM subgroup with benign endometrial conditions, the ratios of the frequency of invasive diagnostic procedures to the incidence of endometrial cancer were higher in subjects under 40 than subjects aged 60 or more.
Conclusion: Symptomatic young breast cancer survivors taking TAM are at a high risk of developing endometrial cancer. Gynecological surveillance should be tailored to the risk of endometrial cancer in young breast cancer survivors to improve the early detection of endometrial cancer and avoid unnecessary invasive procedures.