Recent studies have reported a significant decrease in the expression of ATPase H+/K+ transport β subunit (ATP4B) in gastric cancer,[15, 16, 17, 18, 19] acting as a potential biomarker for malignant transformation in the gastric mucosa.[19] Animal models have further demonstrated that mice with reduced ATP4B mRNA expression exhibit correspondingly lower gastric acid levels.[20] These findings imply that the compromised gastric acidity due to ATP4B downregulation may serve as a functional indicator of gastric cancer, including EGC (Figure1a). This evidence concerns the gene ATP4B and gastric cancer.