Written and medically reviewed by: Assoc. Prof. Cengiz Dibekoğlu, MD, General SurgeryLast updated:
Molecular Testing in Gastric Cancer
HER2, PD-L1, CLDN18.2, and MSI/MMR — timed mainly to advanced therapy, with MSI relevant earlier too.
Advanced gastric/GEJ adenocarcinoma commonly needs HER2, PD-L1 (CPS), and CLDN18.2 testing to choose targeted and immunotherapy combinations. MSI/MMR status can influence care even before classic metastatic lines in selected discussions. Testing volume should match decision points so tissue is not exhausted on low-yield panels. Order tests that answer a stage-specific question rather than collecting unused data. Bring your top three questions to the visit.
Educational schematic. Some structures may be simplified or emphasized for clarity; not an exact anatomical depiction.
© Cengiz Dibekoğlu — illustrative; not for unauthorized use
Figure summary
This educational figure shows: Gastric.
Who may be a candidate?
- International patients preparing a structured second-opinion visit
- Patients comparing observation, medical care, and procedural options
Possible advantages
- Supports informed consent with alternatives and recovery themes
- Highlights red flags that should trigger urgent contact
Limits & realistic expectations
- Cannot replace examination, imaging, or pathology
- Local protocols and tumor-board decisions may refine timing
- Outcomes vary with anatomy, stage, and comorbidity
Step-by-step overview
- 1
Clarify the clinical question
What diagnosis is being confirmed and what decision follows?
- 2
Choose first-line tests
Start with the test that answers the leading question safely.
- 3
Stage if needed
Add imaging or endoscopy when results would change management.
- 4
Name limitations
No test replaces exam; false reassurance is a risk.
- 5
Link to next step
Diagnosis should point to observation, medical care, or procedure.
Key points
- Key note inside
Somatic vs germline
Tumor-only findings are not automatically hereditary. Germline counseling uses separate consent and cascade-testing rules. Discuss timing, alternatives, and follow-up with your surgical team before you finalize a plan.
- Key note inside
Important
This page is for education. It is not medical advice and does not replace a visit with your physician.
Frequently asked questions
Which markers matter most in advanced gastric cancer?
HER2, PD-L1 (CPS), CLDN18.2, and MSI/MMR commonly shape therapy discussions.
Is MSI only for metastatic disease?
MSI/MMR can influence care earlier in selected pathways; ask how it affects your stage.
Why does tissue stewardship matter?
Priority IHC/ISH/NGS can exhaust small samples — coordinate biopsies intentionally.
Can markers change over time?
Sometimes re-biopsy is considered if treatment decisions depend on updated status.
More chapters in this hub
Molecular Testing Overview
Biomarkers answer specific treatment and hereditary questions
Molecular Testing in Colorectal Cancer
MMR/MSI, RAS/BRAF, and selected HER2/NTRK contexts
Molecular Testing in Breast Cancer
ER/PR/HER2 foundations and germline BRCA framework
Molecular Testing in Pancreatic Cancer
Germline testing is discussed for most patients; tumor profiling in advanced disease
Hereditary Cancers
Lynch, BRCA, FAP, CDH1, and genetic counseling in surgical patient language
Appointment / info
This page is for education. It is not medical advice and does not replace a visit with your physician.
Medical editor: Assoc. Prof. Cengiz Dibekoğlu, MD · Last medically reviewed: August 2026 · English patient-education chapter.