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William J. Gradishar, MD, FACP, FASCO


ASCO 2024: Is Adjuvant Endocrine Therapy Necessary for ER-Low Breast Cancer?

By: Julia Cipriano, MS
Posted: Thursday, June 6, 2024

According to Matthew P. Goetz, MD, of the Mayo Clinic, Rochester, Minnesota, and colleagues, the omission of adjuvant endocrine therapy was associated with significantly worse overall survival in patients with estrogen receptor (ER)-low early-stage breast cancer who underwent chemotherapy. Their findings, which were presented during the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting (Abstract 513), advocate for the recommendation of this supplementary treatment both in practice and in clinical guidelines.

“Adjuvant endocrine therapy improves overall survival in patients with hormone receptor–positive early-stage breast cancer,” the investigators commented. “The National Cancer Database began to… allow classification of ER-positive tumors as 1% to 10% [denoting ER-low status] or greater than 10%.” Therefore, the investigators used this database to identify 7,956 patients with stage I to III ER-low disease who received neoadjuvant or adjuvant chemotherapy. Adjuvant endocrine therapy was omitted in 41% of this population.  

At a median follow-up of 3 years, 648 deaths were documented. The 2- and 4-year rates of overall survival were 94.3% and 87.6%, respectively. An unadjusted analysis revealed that omitting adjuvant endocrine therapy was linked to worse overall survival (hazard ratio = 1.40; P < .001), with similar effects regardless of progesterone receptor, HER2, or Ki67 status (each P > .3). After the investigators controlled for age, comorbidity score, year of diagnosis, progesterone receptor and HER2 status, and pathologic stage, they reported that omitting adjuvant endocrine therapy was associated with an adjusted hazard ratio of 1.22 for overall survival (P = .05).

Because overall survival was assessed during the COVID-19 pandemic, with one-third of deaths occurring within the first year of follow-up, the investigators performed a sensitivity analysis of those who survived for at least 1 year after undergoing definitive surgery. The omission of adjuvant endocrine therapy resulted in an adjusted hazard ratio of 1.24 for overall survival (P = .03).

Disclosure: For full disclosures of the other study authors, visit

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