Abstract P4-07-05: Real world data of adjuvant endocrine therapy for breast cancer in very young women. A Chilean 20-year experience
Authors: Heredia Ana , Walbaum Benjamin , Acevedo Francisco , Sánchez Cesar 
Published: March 2023

Abstract
BACKGROUND: Breast cancer (BC) is the most common cancer diagnosed in premenopausal women with an increasing incidence for age 35 or less. Although proportionally less frequent, hormone receptor (HR)–positive BC still remains the main subtype for this group, but given tumor characteristics and suboptimal adjuvant endocrine therapy (ET), present inferior long-term outcomes when compared to HR-positive BC in older women. Both Tamoxifen and Exemestane Trial (TEXT) and Suppression of Ovarian Function Trial (SOFT) have helped to optimize ET strategies for premenopausal women, identifying which patients benefit from ovarian function suppression (OFS). In Chile, we have scarce data on very young BC patients and limited access to proper OFS treatment specially in our public health system. Thus we aim to characterize a cohort of very young women regarding treatment strategies and survival, plus as an exploratory analysis evaluate Regan Score in our cohort.
METHODS We conducted a retrospective population-cohort study involving women under 36 years of age, with early HR-positive/human epidermal growth factor receptor 2 (HER2)–negative BC, treated both at a community hospital and at an academic private hospital between 2001 and 2021. We did a descriptive analysis including stage distribution and treatment strategies (chemotherapy (CT), ET of choice and OFS use). We evaluated prognosis for the entire population. Survival analysis was carried out using the Kaplan-Meier method.
RESULTS A total of 143 patients were included. Median age at diagnosis was 33 (19 - 36); 15.4% percent of patients were diagnosed in stage I, 51.4% stage II and 30.1% stage III. Eighty six percent received CT, 35.0% neoadjuvant. Ninety three percent received endocrine adjuvant treatment: 81.2% TAM alone, 6.8% TAM/OFS and 10.5% IA/OFS. Regarding OFS strategies only 38.5% received gonadotropin-releasing hormone (GnRH) agonists while the rest were oophorectomized. Regan median composite score was 2.77 (2.61 - 2.93) for the entire cohort. Rising to 2.95 (2.79 - 3.11) for patients treated with CT plus ET compared to 1.91 (1.55 - 2.27) for those treated with ET exclusively (p=0.0001). Patients that received TAM alone had a median Regan Score of 2.72 (0.77-4) compared to 3.14 (2.07-4.0) for patients that had OFS added (p=0.04). With a median follow-up of 59 months, 5-year Disease Free Survival (DFS), Distant DFS and Overall Survival (OS) for the entire cohort were 63.5%, 66.9% and 88.7%, respectively.
CONCLUSION. To our knowledge this is one of the largest cohorts considering very young women BC in Latinamerica. We confirm their elevated overall risk with markedly higher Regan scores compared to SOFT and TEXT populations for both CT and ET exclusively treated patients. Due to access difficulties very few patients received OFS and when used, surgical oophorectomy was the main strategy of choice, with all the potential long term consequences it conveys. Thus OFS use was restricted to very high risk women, meaning that a large group of only TAM users were undertreated according to nowadays standards. This could explain the elevated recurrence risk observed in our population when compared to other under 35 years of age cohorts.
Table 1. Cohort characteristics
Table 2. Regan risk score
Citation Format: Ana Heredia, Benjamin Walbaum, Francisco Acevedo, Cesar Sánchez. Real world data of adjuvant endocrine therapy for breast cancer in very young women. A Chilean 20-year experience [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-07-05.