Abstract PS15-04: De-escalation of radiation therapy in patients with stage I, node-negative, HER2-positive breast cancer: Patterns of care and survival outcomes using the national cancer database

Abstract

Background: In the modern era, highly effective anti-HER2 therapy is associated with very low local-regional recurrence (LRR) rates for early-stage HER2+ breast cancer. One recent prospective study of T1-2N0 HER2+ breast cancer patients treated with lumpectomy and adjuvant paclitaxel+trastuzumab followed by whole breast radiation (RT) demonstrated 7-year LRR-free survival of 99% raising the question of whether local therapy de-escalation by RT omission is possible. To evaluate existing data on radiation omission, we used the National Cancer Database (NCDB) to test the hypothesis that RT omission results in equivalent overall survival (OS) in stage 1 (T1N0) HER2+ breast cancer.Materials/Methods: We identified patients with stage I (T1N0) HER2+ breast cancer treated with lumpectomy, adjuvant chemotherapy and anti-HER2 therapy from 2013 (the first year anti-HER2 therapy receipt was reliably collected) to 2015. We excluded patients that received neoadjuvant systemic therapy. We then stratified the cohort by receipt of adjuvant RT. The primary endpoint was OS as LRR is not captured by the NCDB. OS was analyzed by the Kaplan-Meier method (RT and RT omission groups compared by the log-rank test) and multivariate cox regression including variables with p 1 cm vs. ≤1 cm), ER/PR status (ER-/PR- vs. ER+ and/or PR+), facility type (academic vs. non-academic), and income ( 1cm (p=0.14), grade 3 tumors (p=0.14), academic facility (p=0.16) and lower income (p=0.02) but not ER-/PR- status (HR=1.01, p=0.95), distance to treatment facility (p=0.42) or tumor laterality (p=0.66). On multivariate analysis, RT omission (HR=7.55, 95% CI 5.36-10.63, p Citation Format: Jose G Bazan, Sachin Jhawar, Daniel Stover, Ko Un Park, Sasha Beyer, Erin Healy, Julia R White. De-escalation of radiation therapy in patients with stage I, node-negative, HER2-positive breast cancer: Patterns of care and survival outcomes using the national cancer database [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 PS15-04.