Abstract PS3-10-18: Early Discontinuation of Adjuvant Endocrine Therapy in Patients with Triple Positive Early Stage Breast Cancer after Pathologic Complete Response (pCR) to Neoadjuvant Therapy: A Retrospective Review

Abstract Purpose: The current standard of care for patients (pts) with stage 2 or 3 hormone receptor positive (HR+)/ HER2 + breast cancer is neoadjuvant chemotherapy plus HER2-directed therapy (NACT-HP) followed by surgery. For pts who achieve a pCR, anti-HER2 therapy is continued to complete 1 year and pts are recommended to take adjuvant endocrine therapy (ET) for a minimum of 5 years. Adherence to ET can be challenging due to multiple adverse effects that can impair quality of life (QOL). Here we evaluate whether early discontinuation of ET impacts clinical outcomes in a diverse real-world population who achieve pCR following NACT-HP. Methods: A retrospective chart review was conducted for pts with stage 2/3 HR+/HER2+ breast cancer who were treated between 2009 -2020 at the Winship Cancer Institute of Emory University. HR+ was defined as estrogen and progesterone receptor (ER/PR) 1% and HER2 + as IHC 3+ or IHC 2+/FISH positive. Eligible patients received NACT-HP and achieved a pCR. Endpoints were adherence to endocrine therapy (ET) and disease-free survival (DFS), local or distant recurrence, and death. Descriptive statistics were used to summarize demographics and clinical characteristics. Results: Of 40 pts who achieved pCR, 10 (25%) were Black, 28 (70%) were White, 2 (5.0 %) were identified as other. The median follow-up time was 86 months (range: 9-184 months). Of the 40 pts, 24 were age 50 years, and 16 were 50 years. All patients had ER 10%. 13 (32.5%) pts underwent lumpectomy, 16 (40%) underwent bilateral mastectomy, and 11 (27.5%) unilateral mastectomy. Regarding adjuvant ET, 22 (55.0%) pts received an aromatase inhibitor (AI), 9 (22.5%) received tamoxifen, 2 (5.0%) received AI plus ovarian suppression, and 6 (15.0%) received both AI and tamoxifen at various time points. One pt declined ET. Three (7.5%) individuals self-discontinued ET prior to completing 5 years of treatment due to side effects. At the time of follow-up, 36 (80%) patients were disease-free, 3 (7.5%) had recurrence with survival, and 1 (2.5%) had recurrence which led to death. All 3 patients who discontinued ET before 5 years remained disease-free, while the one patient who declined ET died from distant recurrence. Conclusions: In this small, real-world cohort, early discontinuation of adjuvant ET was not associated with disease recurrence. This observation is hypothesis generating and raises the question of whether the recommended 5-year duration of adjuvant ET is necessary in pts who achieve pCR with NACT-HP. With the advent of trials like the LoTamTrial exploring de-escalation of adjuvant ET, it is prudent to highlight real-world evidence of distant recurrence following early ET discontinuation. While our findings are limited by a small cohort size and retrospective nature, a larger cohort will be updated prior to the meeting, also including patients treated between 2020 to present. Citation Format: A. Hadadi, W. Yang, X. Yi, E. A. Sakach, J. Meisel. Early Discontinuation of Adjuvant Endocrine Therapy in Patients with Triple Positive Early Stage Breast Cancer after Pathologic Complete Response (pCR) to Neoadjuvant Therapy: A Retrospective Review 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 PS3-10-18.