In a study reported in the Journal of Clinical Oncology, Choong et al found that omission of endocrine therapy in patients with estrogen receptor–low (1%–10% on immunohistochemistry), early-stage breast cancer was not associated with improved survival outcomes. The study used National Cancer Database data on patients with high-risk, stage I–III, estrogen receptor–low breast cancer who received (neo)adjuvant chemotherapy and did or did not initiate endocrine therapy.
Key Findings
Among 10,362 patients identified with stage I–III estrogen receptor–low breast cancer, 7,018 received chemotherapy and were included in the analysis.
Estrogen therapy omission was 42% at 12 months and more common in patients with tumors that were progesterone receptor–negative, HER2-negative, and higher-grade (grade 2–3) and had a higher Ki67 index (≥ 20%; all P < .001) and in patients who received neoadjuvant chemotherapy (P < .001).
At a median follow-up of 3 years, 586 deaths were observed. In multivariate analysis, endocrine therapy omission was associated with an increased risk of death (hazard ratio [HR] = 1.23, 95% confidence interval [CI] = 1.04–1.46, P = .02); greater risk was observed among patients with estrogen receptor 6%–10% (HR =1.42, 95% CI = 1.00–2.02, P = .048) compared with those with estrogen receptor 1%–5% (HR = 1.15, 95% CI = 0.91–1.45, P = .24).
Among 4,377 patients treated with neoadjuvant chemotherapy (62%), endocrine therapy omission was associated with worse overall survival in those with residual disease (HR = 1.26, 95% CI = 1.00–1.57, P = .046) but not in those with a pathologic complete response (HR = 1.06, 95% CI = 0.62–1.80, P = .84).
The investigators concluded: “In [estrogen receptor]–low, early-stage [breast cancer], [estrogen therapy] omission is associated with significantly worse [overall survival], especially in patients with [residual disease] after [neoadjuvant chemotherapy] and those with higher (6%–10%) [estrogen receptor] levels. Until prospective data are available, patients with [estrogen receptor]–low [breast cancer] should be counseled regarding the potential benefit of [estrogen therapy].”
Matthew P. Goetz, MD, of the Department of Oncology, Mayo Clinic, Rochester, Minnesota, is the corresponding author of the Journal of Clinical Oncology article.
Disclosure: The study was supported by a grant from the National Cancer Institute. For full disclosures of all study authors, visit the Journal of Clinical Oncology.
