Abstract PO1-01-12: A retrospective cohort study on the effect of adding adjuvant ovarian function suppression to endocrine therapy in premenopausal women with T1-T2 tumor hormone-positive breast cancer on survival and disease recurrence

Abstract Background: Breast cancer is the most common diagnosed cancer in women and is the leading cause of cancer death. Young women diagnosed with breast cancer are at higher rates of adverse outcomes in terms of survival and recurrence. Hormone sensitive breast cancer is the commonest subtype of breast cancer in this group. To date, the standard adjuvant treatment is endocrine therapy for both pre and post-menopausal women. Recent published studies have recommended adding ovarian function therapy to premenopausal women who are at high risk of recurrence. In this study we evaluated the impact of adding adjuvant ovarian function suppression for premenopausal women with small (T1 and T2) hormone receptor positive node negative breast cancer who did not receive any form of chemotherapy on overall survival and disease-free recurrence. Methods: We performed a retrospective study where we evaluated the electronic medical records of 4431 premenopausal women diagnosed with breast cancer in Asan Medical Center in Seoul, South Korea. All the analyzed patients were operated from the period of January 2006 till December 2019. The inclusion criteria were age of 55 and below, T1 and T2 tumors with N0 disease who received selective estrogen receptor modulators (SERM - Tamoxifen) and didn’t receive neo or adjuvant chemotherapy. We compared patients who received SERM (Tam Only) only to patients who received SERM and ovarian function suppression (Tam + OFS) medications. The primary endpoint was overall survival (OS), and the secondary endpoint was mortality and disease-free survival (DFS). We used chi-square test for categorical variables and t-test for continuous variables. The p-value was set as p 0.05 as statistically significant. Kaplan Meier curve and log rank test were used to analyze the data for overall survival, disease-free survival and mortality. We performed an additional subgroup analysis adjusted to age, tumor size, Ki67%, progesterone receptor, HER2 status and type of operation. Results: There was equal distribution of cases between tamoxifen only group and tamoxifen + OFS group (2121 versus 2310 respectively). The median age in each group was 45 years of age. Tumor size of ≤0.5cm was the commonest in the tamoxifen only group whereas tamoxifen + OFS group had majority of cases with tumor size of 1 - 2cm. Both groups had a Ki-67% of 10-20%. Histologic grade of 2 and nuclear grade of 2 were most commonly representative in the comparing groups. Invasive ductal carcinoma was the most common histological subtype (93-94%) and invasive lobular carcinoma accounted for 5-6% of cases. Regarding immunohistochemistry results, 91-93% of patients were progesterone receptor positive and 68-73% were HER2 negative. The majority underwent breast conserving surgery compared to mastectomy. We have also looked at the pattern of prescribing OFS treatment in the Tamoxifen + OFS group regarding the length of treatment. Nearly 80% of patients received OFS treatment for a period of 1-2 years whereas only 5.2% received 1 year and 1.8% 2years. After adjusting to age, tumor size, Ki67%, PR receptor and HER2 status, the result was only significant for higher risk of DFS in the TAM + OFS group in Ki67 20%. The OFS+TAM had more DFS and mortality events compared to TAM only group. However, the only significant result was the overall survival favoring tamoxifen only group with a p-value of 0.039 and HR of 1.05-7.99. Conclusion: Adding ovarian function suppression to tamoxifen in premenopausal hormone positive node negative T1-T2 tumors didn’t show any benefit in terms of disease-free interval and overall survival. Further studies are advised to assess the benefit of adding ovarian function suppression to this group of patients Table 1: baseline characteristics of Table 2: Disease Free Survival Subgroup Analysis Citation Format: Sarah Al Safi, Hee Jeong Kim, Seonok Kim, Sae Byul Lee, Jisun Kim, Tae-Kyung Yoo, Il-Yong Chung, Beom Seok Ko, Byung Ho Son. A retrospective cohort study on the effect of adding adjuvant ovarian function suppression to endocrine therapy in premenopausal women with T1-T2 tumor hormone-positive breast cancer on survival and disease recurrence abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-01-12.