Extracellular Vesicles-Associated tRFs as Emerging Biomarkers in Breast Cancer

Breast cancer (BC) remains a leading cause of cancer-related mortality among women worldwide, underscoring the urgent need for sensitive, non-invasive biomarkers to improve diagnosis, prognosis, and treatment monitoring. Traditional biomarkers like ER, PR, and HER2 offer limited efficacy, particularly for heterogeneous subtypes such as triple-negative breast cancer (TNBC). Extracellular vesicles (EVs), including exosomes and microvesicles, have emerged as promising biomarker carriers due to their stability and ability to encapsulate diverse bioactive molecules reflective of the parental cell's state. Among EV cargoes, tRNA-derived fragments (tRFs), which are small non-coding RNAs produced by precise cleavage of tRNAs, have gained increasing attention. Once considered mere degradation products, tRFs are now recognized for their roles in gene regulation, translation control, apoptosis modulation, and immune response. Recent studies have revealed the selective enrichment of tRFs within EVs, highlighting their role in intercellular communication in breast cancer. Differential expression of EV-associated tRFs correlates with BC subtype, stage, and patient prognosis, highlighting their potential as minimally invasive biomarkers. Specifically, altered levels of certain 5'- and 3'-tRFs in patient sera and tumor tissues have been associated with poor survival, metastasis, and therapeutic resistance. Despite these promising findings, gaps remain regarding the mechanisms of tRF sorting into EVs and their functional impact on the tumor microenvironment. This review systematically examines the current understanding of EV-associated tRFs in breast cancer, emphasizing their clinical relevance, detection strategies, and translational potential. By addressing existing challenges, we aim to provide insights into the utility of EV-tRFs as novel biomarkers and therapeutic targets in BC.