Serum Exosomal ADGRF5: A Potential Diagnostic Biomarker for Metastasis in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is associated with frequent recurrence, early metastasis, and poor prognosis, making timely detection of metastatic spread clinically important. Because exosomes are involved in tumor metastasis and immune evasion, they may provide useful early biomarkers. This study aimed to identify and preliminarily validate serum exosomal markers for TNBC metastasis using high-throughput proteomics. Two sequential, independent 4D-label free proteomic analyses of serum exosomes were performed. The exploratory phase used pooled serum samples from 6 metastatic TNBC patients, 6 nonmetastatic TNBC patients, and 6 healthy controls, generating 9 exosome samples. A second analysis was conducted in an expanded cohort of 10 metastatic and 10 nonmetastatic TNBC patients. Differentially expressed proteins identified in both analyses were compared and further evaluated by Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and receiver operating characteristic analyses, with selected candidates validated by ELISA. Distinct exosomal protein expression profiles were observed among metastatic TNBC, nonmetastatic TNBC, and healthy controls. ADGRF5 showed strong diagnostic performance in distinguishing metastatic from nonmetastatic TNBC, with an area under the curve of 0.94. These findings suggest that ADGRF5 is a promising serum biomarker for TNBC metastasis and may aid future breast cancer biomarker discovery.