Gastric cancer remains the fourth leading cause of cancer deaths globally, yet treatment outcomes are improving dramatically as pathologists gain precision tools to match therapies to tumor biology. The molecular fingerprint of each gastric tumor now determines whether patients receive targeted HER2 inhibitors, immune checkpoint blockers, or conventional chemotherapy.
This comprehensive analysis examines how immunohistochemistry techniques identify three critical biomarkers that guide treatment decisions. HER2 protein overexpression, found in roughly 15-20% of gastric cancers, predicts response to trastuzumab-based therapies. PD-L1 expression levels help oncologists select patients most likely to benefit from pembrolizumab or nivolumab immunotherapy. DNA mismatch repair deficiency, present in about 4% of cases, indicates exceptional responsiveness to immune checkpoint inhibition. Advanced DAB staining protocols now provide more reliable detection of these molecular targets.
The review highlights emerging challenges in gastric cancer classification, particularly aggressive histological subtypes that resist standard treatments. Epithelial-mesenchymal transition markers and E-cadherin loss patterns are revealing new therapeutic vulnerabilities, while tumor budding assessment helps predict metastatic potential.
This represents a fundamental shift from treating gastric cancer as a single disease to recognizing distinct molecular subtypes requiring different approaches. The precision becomes especially critical given gastric cancer's poor overall prognosis—five-year survival rates remain below 35% in most countries. However, patients whose tumors express the right biomarkers increasingly achieve long-term remissions with targeted therapies, transforming what was once universally fatal into a manageable chronic condition for select cases.