NCDB analysis of endocrine therapy omission in estrogen receptor-low early stage breast cancer

Endocrine therapy (ET) is recommended for estrogen-receptor (ER)-positive breast cancer (BC), although its benefit in ER-low (1-10%) disease is uncertain. Analysis of the National Cancer Database (NCDB) evaluated the impact of ET omission on survival in ER-low disease. The analysis included female patients with stage I-III ER-low BC diagnosed between 2018 and 2023 who were treated with neoadjuvant chemotherapy (NAC) and or adjuvant chemotherapy. Among 12,983 patients, 8658 received NAC (53% achieved pCR) and 4325 received adjuvant chemotherapy alone. ET use declined significantly over time, for 62% in 2018 versus 33% in 2023; p<0.001), with the greatest decline among NAC-treated patients. Overall survival (OS) analysis included 11,136 patients (median follow-up 3.4 years; 1137 deaths). ET omission was associated with worse OS (aHR 1.24; p<0.001), particularly in patients with residual disease after NAC. ET omission was associated with worse survival in both ER 1-5% and ER 6-10% subgroups. The authors conclude that ET use in ER-low BC treated with chemotherapy is declining, while ET omission in this population is associated with worse OC.