Abstract PS3-08-23: Endocrine resistance: prevalence and outcomes in hispanic women with early breast cancer

Abstract Background: Hormone receptor (HR)-positive early breast cancer (EBC) accounts for 60-70% of cases (1). However, EBC experience probability of recurrence rate of 3%, which reflects endocrine resistance (ER). The impact of ER on clinical outcomes has not been thoroughly examined in EBC, especially in the hispanic population, despite their increased vulnerability and disproportionate burden of disease. Methods: Retrospective analysis of 1,551 ER(+)-EBC patients at from 2007 to 2017. Data on clinico-pathologic and treatment variables were collected from electronic medical records. Recurrence cases classified: primary endocrine resistance (1ER) within 24 months,secondary endocrine resistance (2ER) between 24-60 m, and endocrine-sensitive recurrence (3ESR) after 60 m of relapse. Descriptive statistics defined the population's general characteristics. Differences were analyzed with Chi-square for categorical variables and t-tests for continuous variables. The Kaplan-Meier method and log-rank test were applied for survival analysis, while Cox regression for multivariate analysis. A p-value < 0.05 indicated statistical significance. Results: Patients had a median age of 52.2 years (IQR 45.0-62.0). 574 (37%) were premenopausal,and 343 (22%) had a high nodal burden (N2/N3). In a median follow-up of 9.1 years (IQR5.9-12.0), 392 patients (25%) experienced recurrence, with an annual rate of 3-5% during the first five years. Among them, 128 patients (33%) had 1ER, 182 (46%) had 2ER, and 82(21%) had 3ESR. Table 1 displays population characteristics at recurrence. Clinical stage III, Grade 3, and H-Score expression of estrogen and progesterone receptors varied significantly among the subgroups. Oncotype was conducted in 130 patients, with median scores of 29 for 1ER, 24 for 2ER, 19 for 3ESR, and 14 for the non-recurrent group(p<0.001). At 10 years, overall survival (OS) rates for 1ER, 2ER, and 3ESR were 13%, 32%, and 79%, respectively (p<0.0001). Even in cases of metastatic visceral disease, OS rates show significant differences: 37, 80, and 173 months in the 1ER, 2ER, and 3ESR subgroups respectively (p<0.0001). Multivariate analysis for OS show the risk of death for women with 1ER HR 12.7; 95% CI (8.12-20.00) and compared to secondary resistance HR 4.4; 95% CI (2.81-6.8), as well as in those patients with visceral metastatic disease HR 1.7 95% CI (1.33-2.2) p<0.001. Conclusions: Our study found higher relapse rates and endocrine resistance, potentially due to delays in diagnosis and clinical risk. Women with 1ER had a higher mortality risk. This analysis highlights the need to improve early diagnosis, equal access to adjuvant CDK4/6 therapies, and enhance surveillance strategies in high clinical risk EBC. Citation Format: A. V. Martinez, P. A. Cabrera-Galeana, A. Mohar-Betancourt, J. E. Hernandez-Hernandez, C. A. Gonzalez-Reyes, A. Maliachi-Diaz, A. Garcilazo-Reyes, E. Bargallo-Rocha, C. H. Arce-Salinas, D. F. Flores-Diaz. Endocrine resistance: prevalence and outcomes in hispanic women with early breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS3-08-23.