REXO1 (RNA exonuclease 1 homolog) is a nuclear protein with exonuclease activity involved in rRNA 3'-end processing 1. Located in nuclear bodies and the nucleoplasm, REXO1 shares structural similarity with transcription elongation factors but has no detectable effect on transcription elongation in vitro 1. REXO1 was originally identified as Elongin A-binding protein 1 (EloA-BP1) through its interaction with the Elongin complex, suggesting potential regulatory roles in transcription that may manifest in vivo despite lacking measurable in vitro activity 1. Clinically, REXO1 has emerged as a biomarker for cancer risk. Increased DNA methylation in genomic regions associated with REXO1 in prospectively collected blood samples predicted breast cancer development up to 15 years before clinical diagnosis, with a machine learning classifier achieving 76.5% accuracy in case-control prediction 2. Additionally, REXO1L1 (a homologous gene cluster) copy number variation has been associated with potential susceptibility to hepatitis C virus infection, though this relationship requires further investigation 3. These findings suggest REXO1 participates in cancer-associated epigenetic changes detectable in peripheral blood, offering potential applications for early risk stratification and personalized cancer prevention strategies.