Abstract PS5-30: Effect of level of hormone-receptor expression on treatment outcomes of “triple-positive” early-stage breast cancer

Introduction: 20-25% of breast cancers overexpress the human epidermal growth factor receptor-2 (HER2) and have an aggressive clinical behavior; 50-70% of them also express both estrogen (ER) and progesterone (PR) receptors. Multiple regulatory and signaling pathways regulate and affect breast cancer response to various therapies. Breast cancer that overexpress HER2 and both ER and PR receptors, which represents nearly 10-15% of all breast cancers, are recently recognized as a subtype (triple-positive: TPBC) with distinctive behavior and response to treatment. However, the idea of separating this type of breast cancer according to the level of ER and PR expression is still debated. In this study, we retrospectively investigate the clinical features and treatment outcomes of early-stage TPBC patients treated at a tertiary care center, and how survival patterns are affected by levels of HR expression. Methods: Adult patients with pathologically confirmed diagnosis of early-stage (stage I-III) TPBC were included. ER or PR were considered positive if staining of tumor cell nuclei was ≥ 1%. Due to drug approval and availability, 50 (16.0%) patients (Cohort A) had not received trastuzumab throughout their treatment and were treated with chemotherapy alone (anthracycline and taxane-based regimens). The rest of the patients received standard adjuvant chemotherapy and trastuzumab and were divided based on level of HR expression into two cohorts; patients whose immunohistochemical staining displayed ≥ 50% in both ER and PR scores were classified as Cohort B and constituted 41.7% of the study population (n=130) while patients who displayed Citation Format: Hikmat Abdel-Razeq, Sarah Edaily, Sereen Iweir, Mourad Salam, Yacob Saleh, Maher Sughayer, Osama Salama, Rawan Mustafa, Yosra Almasri, Rayan Bater, Ayat Taqash. Effect of level of hormone-receptor expression on treatment outcomes of “triple-positive” early-stage breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS5-30.