RLN1 (relaxin 1) encodes a peptide hormone that functions primarily in reproductive processes and tissue remodeling, with emerging roles in cancer biology. RLN1 acts through binding to the relaxin family peptide receptor 1 (RXFP1, also known as LGR7) to mediate anti-fibrotic effects and extracellular matrix remodeling 1. The gene shows tissue-specific expression, with high levels in prostate tissue, and can form novel fusion transcripts with RLN2 in prostate cancer 2. In heart failure with reduced ejection fraction, elevated circulating RLN1 levels correlate inversely with myocardial fibrosis, suggesting a protective anti-fibrotic role 1. However, RLN1 also promotes cancer progression through multiple mechanisms including increased cell proliferation, invasion, and adhesion while decreasing apoptosis 3. In breast cancer, RLN2 (but not RLN1) is directly regulated by estrogen receptor-alpha, with expression increasing cancer cell invasiveness 4. Despite high transcript levels in cancer cell lines, endogenous RLN1 protein is often undetectable by sensitive immunoaffinity-mass spectrometry methods, raising questions about post-transcriptional regulation 5. The dual role of RLN1 as both a protective anti-fibrotic factor and cancer promoter highlights its complex biological functions.