MUC4 is a membrane-bound mucin that functions as a highly glycosylated epithelial protection factor and cellular signaling modulator. As a major mucus component, MUC4 protects epithelial surfaces and promotes epithelial renewal and differentiation 1. Beyond its structural role, MUC4 acts as an intramembrane ligand for ERBB2, regulating proliferation and differentiation through phosphorylation cascades 2. MUC4 expression is upregulated during mucociliary differentiation of airway epithelia in a retinoic acid-dependent manner 3 and is induced in metaplastic pit cells during Helicobacter pylori-driven gastric inflammation 4. In cancer pathology, MUC4 is a clinically significant marker with dual importance. It is rarely expressed in normal pancreas but extensively overexpressed in pancreatic tumors, making it a valuable tumor-associated antigen for vaccine development 5. MUC4 expression correlates with aggressive tumor behavior and poor prognosis in various neoplasms 6. The protein's upregulation in precancerous lesions and association with enhanced proliferation in gastric cancer 4 suggest its utility in early cancer detection. MUC4 has therapeutic potential as an immunotherapy target and biomarker for evaluating malignancy potential, particularly in pancreatobiliary and gastric cancers 6, 5.