RLN2 (relaxin-2) is a peptide hormone with dual roles in reproductive physiology and pathological processes. In normal physiology, RLN2 mediates connective tissue remodeling during pregnancy, promoting cervical ripening and pubic ligament growth through collagen degradation and matrix metalloproteinase upregulation 1. RLN2 signals via the G protein-coupled receptor RXFP1 to trigger vasodilation, angiogenesis, and anti-inflammatory effects 2. In cancer pathogenesis, RLN2 expression is frequently elevated and contributes to aggressive phenotypes across multiple malignancies. In breast cancer, estrogen receptor-alpha directly regulates RLN2 transcription 3, and tumor-associated neutrophils secrete RLN2 to suppress the immune lncRNA C6orf99 via RXFP1, activating pro-tumoral STAT3 signaling 4. In osteosarcoma, RLN2 promotes cell invasion and chemoresistance through AKT/NF-κB pathway activation 5, and elevated RLN2 expression correlates with metastasis and poor survival 6. RLN2 is also upregulated in thyroid carcinoma tissues 7 and prostate cancer, where novel RLN1-RLN2 fusion transcripts are detected 8. Clinically, RLN2's antifibrotic properties show therapeutic promise: engineered long-acting RLN2 variants maintain RXFP1 agonist activity for heart failure and fibrotic disease treatment 2, while RLN2-secreting CAR-T cells enhance tumor infiltration in stroma-rich solid tumors 1. RLN2 represents both a cancer biomarker and potential therapeutic target.