A Novel Protein Serum Biomarker Assay for Tracking (Neo)adjuvant and Metastatic Therapy Efficacy and Enabling the Timely Detection of Relapse in Breast Cancer

Objectives: There is high interest in blood-based assays for tracking treatment efficacy and detecting recurrence among breast cancer patients. This preliminary feasibility study assessed the performance of the Early Detection Serum-based Assay for Breast Cancer (EDSA-BC), which measures a novel protein biomarker (BF-09), in (neo)adjuvant and metastatic treatment follow-up. Methods: In total, 313 serial serum samples collected retrospectively from 72 BC patients (72.2% stage I–III, 27.8% stage IV) during disease management (median 33.4 months) were analyzed for BF-09 serum level at different time points before and/or after surgery and treatment (3 to 9 samples per patient). Serial dynamics of BF-09 were correlated with clinically recorded outcomes. Results: Per-sample performance of EDSA-BC for progressive disease or recurrence was 74% sensitivity at 85% specificity with 49.4% positive predictive value, 94.3% negative predictive value and 83% accuracy. Median lead time in detecting relapse was 9.4 months (range 0.8–27 months). Conclusions: Results showed the clinical validity of BF-09 in reflecting relative tumor burden and were comparable to tumor-naïve ctDNA liquid biopsy, especially as a single-marker test. These findings indicate that EDSA-BC has potential as a scalable and cost-efficient assay to aid in breast cancer management. Prospective studies are needed to clarify sampling tempo, clinical utility and benefit.