It serves not only as a significant biomarker for early hepatocellular carcinoma screening, liver fibrosis assessment, and immunotherapy response prediction, but also reveals novel therapeutic dimensions through recently identified mechanisms—specifically, macrophage-derived OPN alleviates hepatic steatosis via activation of the OSM–STAT3–ARG2 signaling axis. The gene discussed is ARG2; the disease is hepatocellular carcinoma.