Endocrine Therapy Omission in Estrogen Receptor–Low (1%-10%) Early-Stage Breast Cancer

Author(s): Grace M. Choong, MD1; Tanya L. Hoskin, MS2; Judy C. Boughey, MD3; James N. Ingle, MD1; Matthew P. Goetz, MD1;
Source: J Clin Oncol. 2025;43(16):1875-1885

Dr. Maen Hussein's Thoughts

DON’T omit, there is still a benefit, especially in 6-10% patients.

PURPOSE

Adjuvant endocrine therapy (ET) improves overall survival (OS) in estrogen receptor (ER)–positive early-stage breast cancer (BC). However, the benefit of ET for those with ER-low BC (ER 1%-10%) is unclear.

METHODS

Using the National Cancer Database, we studied patients with high-risk stage I to III, ER-low BC (defined as immunohistochemistry 1%-10%) who received (neo)adjuvant chemotherapy and did or did not initiate ET. OS was analyzed with ET initiation as a time-dependent covariate using Cox proportional hazards regression.

RESULTS

Of 10,362 patients with stage I to III ER-low BC, 7,018 received chemotherapy and met inclusion criteria. ET omission was 42% at 12 months and more common in patients with tumors that were progesterone receptor–negative, human epidermal growth factor receptor 2–negative, higher-grade (grade 2/3) and higher Ki-67 (≥20%; all P < .001) and those who received neoadjuvant chemotherapy (NAC; P < .001). With a median follow-up of 3 years, 586 deaths were observed. In a multivariable analysis, ET omission was associated with a higher risk of death (hazard ratio [HR], 1.23 [95% CI, 1.04 to 1.46]; P = .02), with a greater impact in those with higher ER levels: ER 1%-5% (HR, 1.15 [95% CI, 0.91 to 1.45]; P = .24) versus ER 6%-10% (HR, 1.42 [95% CI, 1.00 to 2.02]; P = .048). Among patients treated with NAC (n = 4,377, 62%), ET omission was associated with worse OS in those with residual disease (RD; HR, 1.26 [95% CI, 1.00 to 1.57]; P = .046) but not in those who achieved a pathologic complete response (HR, 1.06 [95% CI, 0.62 to 1.80]; P = .84).

CONCLUSION

In ER-low, early-stage BC, ET omission is associated with significantly worse OS, especially in patients with RD after NAC and those with higher (6%-10%) ER levels. Until prospective data are available, patients with ER-low BC should be counseled regarding the potential benefit of ET.

Author Affiliations

1Department of Oncology, Mayo Clinic, Rochester, MN; 2Division of Clinical Trials and Biostatistics, Mayo Clinic, Rochester, MN; 3Division of Breast and Melanoma Surgical Oncology, Mayo Clinic, Rochester, MN;

Leave a Comment

Your email address will not be published. Required fields are marked *

Related Articles

Vepdegestrant, a PROTAC Estrogen Receptor Degrader, in Advanced Breast Cancer

Vepdegestrant is an oral proteolysis-targeting chimera (PROTAC) estrogen receptor (ER) degrader that directly utilizes the ubiquitin–proteasome system. It was compared to fulvestrant in patients who had received one prior line of hormonal therapy with a CDK4/6 inhibitor. Among patients with ESR1 mutations, Vepdegestrant demonstrated a median progression-free survival (PFS) of 5.0 months versus 2.1 months with fulvestrant. In the overall population, the median PFS was 3.8 months for Vepdegestrant and 3.6 months for fulvestrant, indicating that the drug showed particular efficacy in tumors harboring ESR1 mutations.

Read More »

Elinzanetant for Vasomotor Symptoms from Endocrine Therapy for Breast Cancer

Elinzanitant, a neurokinin-targeted therapy, has been shown to reduce vasomotor symptoms compared to placebo. These symptoms are one of the reasons some of my patients discontinue aromatase inhibitor (AI) therapy, so Elinzanitant presents a promising alternative to help manage these side effects. Additionally, Fezolinetant is already approved and available on the market.

Read More »

Overall Survival with Inavolisib in PIK3CA-Mutated Advanced Breast Cancer

The INAVO120 trial evaluated inavolisib + palbociclib–fulvestrant vs placebo + palbociclib–fulvestrant in patients with PIK3CA-mutated, HR+/HER2– advanced breast cancer progressing on or shortly after adjuvant endocrine therapy (ET). Inavolisib significantly improved overall survival (OS) (34.0 vs 27.0 mo) and progression-free survival (PFS) (17.2 vs 7.3 mo), with a higher objective response rate (ORR) (62.7% vs 28.0%) and longer DoR (19.2 vs 11.1 mo). Toxicities were manageable but included more hyperglycemia (63.4%), stomatitis (55.3%), GI, and ocular AEs. Bottom line: this triplet sets a new bar for first-line PIK3CA-mutant HR+ MBC, but we’ll need to stay vigilant about metabolic and mucosal side effects as we bring it into practice.

Read More »