REG1A (regenerating family member 1 alpha) is a secreted protein that functions as a growth factor and antimicrobial peptide with roles in tissue regeneration and host defense. The protein is induced by IL-22 signaling and expressed in various cell types including enterocytes, goblet cells, Paneth cells, and stem cells, where it contributes to antimicrobial host defense responses 1. REG1A demonstrates protective functions against cellular damage, specifically preventing blue light-induced apoptosis in retinal photoreceptors by upregulating anti-apoptotic gene Bcl2 and downregulating pro-apoptotic Bax, thereby reducing mitochondrial damage 2. The protein serves as a biomarker for multiple diseases, with elevated circulating levels associated with pancreatic cancer risk and potential causal effects supported by Mendelian randomization analysis 3. In diabetic kidney disease, REG1A expression correlates with disease severity and serves as a predictive biomarker 4. REG1A expression in cancer contexts shows tissue-specific effects: in hepatocellular carcinoma, it associates with more advanced disease when co-expressed with PAP 5, while in urothelial carcinoma, its expression correlates with higher tumor stage and recurrence 6. Additionally, REG1A is a marker of signet ring cell precursors in hereditary diffuse gastric cancer 7.