A Real-World Data Retrospective Cohort Study of Low Estrogen Receptor-Positive Early Breast Cancer: Natural History and Treatment Outcomes

Abstract

Shahla Bari,1 David Boulware,2 Jiannong Li,2 Loretta Loftus,3 Aixa Soyano Muller,3 Zena Jameel,4 Hung Khong,3 Brian J Czerniecki,3 Ricardo LB Costa3 1Department of Hematology/Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA; 2Department of Biostatistics, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA; 3Department of Breast Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA; 4Department of Anatomic and Clinical Pathology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USACorrespondence: Ricardo LB Costa, Department of Breast Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA, Tel [phone], Fax [phone], Email [email protected]: Estrogen receptor-positive (ER+) breast cancer (BC) is a heterogeneous disease, and there is an ongoing debate regarding the optimal cut point for clinically relevant ER expression. We used a real-world database to assess the prognostic and predictive values of lower ER expression levels on treatment outcomes with endocrine therapy.Methods: We used a nationwide electronic health record database. Descriptive statistics were used to evaluate the association between ER expression, tumor characteristics, and treatment patterns among patients with early-stage BC. We used Kaplan–Meier survival curves to estimate recurrence-free survival (RFS) and overall survival (OS). We assessed associations between an alternative ER expression-level cut point and clinical outcomes.Results: Among 4697 patients with early-stage HER2-negative BC, 83 (2.04%) had ER+-low BC (ER expression, 1– 9.99%) and 36 (0.88%) had ER+-intermediate BC (10– 19.9%). ER+-low tumors were associated with higher tumor grade, larger size, and higher axillary tumor burden than ER+-high tumors (≥ 20% ER expression). African Americans had a higher prevalence of both triple-negative BC (TNBC) and ER+-low BC than ER+-high BC. Patients with ER+-low and ER+-intermediate tumors had survival outcomes similar to patients with TNBC and worse survival outcomes than patients with ER+-high tumors (P < 0.001). Tumors with < 20% ER expression were associated with worse outcomes.Conclusion: In our cohort, patients with BCs with ER expression levels < 20% had poor clinical outcomes similar to those of patients with TNBC.Keywords: breast cancer, estrogen receptor, low-positive, recurrence-free survival

Keywords

• breast cancer
• estrogen receptor
• low-positive
• recurrence-free survival.