P-317 Risk of endometrial polyps and hyperplasia after tamoxifen treatment in women with breast cancer: a population-based study in Taiwan

Abstract Study question This study aimed to examine the association between tamoxifen treatment and incident risks of uterine disease among breast cancer patients in Taiwan. Summary answer We found tamoxifen treatment group may have greater risk of endometrial polyps and hyperplasia than unexposured group after adjusting for age and body mass index. What is known already In the worldwide Adjuvant Tamoxifen: Longer Against Shorter (ATLAS) breast cancer treatment trail reported that the women continue tamoxifen up to 10 years, compared with 5 years may reduce breast cancer recurrence and mortality rate. However, tamoxifen use has been reported to be associated with the cumulative risk of subsequently endometrial cancer during 5–14 years was 3.1%. Specifically, several Western studies have showed that the high incidence of endometrial cancer in breast cancer survivors with tamoxifen treatment. Study design, size, duration We conducted a retrospective cohort study using population-based data from Taiwan Cancer Registry and the National Health Insurance Research Database (NHIRD), and the National Population Registry Data set from 2011 to 2020. Participants/materials, setting, methods A total 138,934 newly diagnosed breast cancer female patients with age greater than 18 years old were included. We further used a 1-to-1 propensity score matching to generate comparable exposure and un-exposure groups. Cox proportional hazard regression models were used to examine the research question. All statistical analysis was performed using SAS version 9.4, and p-values 0.05 were considered statistically significant Main results and the role of chance Incidence rate ratio (IRR) to compare incidence rate of uterine disease between tamoxifen treatment groups and unexposed group, adjusting for age and BMI. Our results showed that IRR were 1.36, 0.33, 3.73, 0.63, endometrial polyps, endometrial carcinoma, endometrial hyperplasia and uterine carcinosarcoma, respectively. This study found possible correlations between tamoxifen exposure with endometrial polyps and hyperplasia among breast cancer. During the 10-year study period, tamoxifen group did not significantly increase the risk of endometrial cancer in breast cancer survivors at aged 40 and over. Limitations, reasons for caution Our cohort study with 10-year period is its short study period, Tamoxifen group did not significantly increase the risk of endometrial cancer. Wider implications of the findings This cohort study found higher endometrial polyps and hyperplasia incidence rates among women with breast cancer who received tamoxifen women than those not treated with tamoxifen. Results of this study suggest that clinicians should consider the risk of uterine disease among tamoxifen use and counsel patients accordingly. Trial registration number KMUHIRB-G(II)20200217