MSRA (methionine sulfoxide reductase A) is a protein repair enzyme that catalyzes the reversible reduction of methionine sulfoxide residues back to methionine, restoring function to proteins damaged by oxidative stress. The enzyme operates across multiple cellular compartments including the cytosol, mitochondria, and nucleoplasm, functioning as part of the broader cellular antioxidant defense system alongside thioredoxin and glutathione pathways 1. In cancer biology, MSRA acts as a metastasis suppressor in pancreatic ductal adenocarcinoma. MSRA expression is decreased in metastatic tumors, and its loss promotes cell migration and invasion by allowing selective oxidation of methionine residues (specifically M239) in pyruvate kinase M2 (PKM2), sustaining PKM2 in an active state that enhances cellular respiration and metastatic potential 2. In nonsmall cell lung cancer, a protective MSRA variant (rs73534533 C>A) is associated with improved overall survival, with differential expression analysis showing lower MSRA mRNA levels in both lung squamous carcinoma and adenocarcinoma compared to adjacent normal tissue 3. Recent evidence suggests that MSRA-mediated reduction of oxidized methionine on mutant EGFR can influence resistance to tyrosine kinase inhibitors in NSCLC 4. Additionally, genetic variants in MSRA influence personality traits and irritability across multiple domains 5, suggesting broader roles in neurobiological function beyond oxidative stress response.