What biomarker tests are recommended for Stomach Cancer

Biomarker Testing for Stomach Cancer

Based on the NCCN Guidelines for Gastric Cancer (Version 3.2025), here are the biomarker tests recommended for newly diagnosed stomach cancer patients:

Universal Testing (Recommended for All Patients)

According to NCCN Guidelines, all newly diagnosed stomach cancer patients should receive:

1. Microsatellite Instability (MSI) Testing

   • Tests for errors in DNA copying that occur in small DNA segments
   • Method: PCR (polymerase chain reaction) or next-generation sequencing (NGS)
   • Why it matters: Patients with MSI-high (MSI-H) tumors may be candidates for immunotherapy drugs like pembrolizumab (Keytruda)

2. Mismatch Repair (MMR) Status

   • Tests the cell's ability to correct those DNA copying errors
   • Method: Immunohistochemistry (IHC)
   • Why it matters: Deficient MMR (dMMR) also opens doors to immunotherapy options

3. PD-L1 Expression Testing

   • Measures a protein (PD-L1) on cancer cells that helps them hide from the immune system
   • Method: Immunohistochemistry
   • Why it matters: PD-L1 status helps determine if immunotherapy will be effective

Testing for Advanced/Metastatic Disease

If your cancer has spread or is advanced, your doctor should also test for:

1. HER2 Status

   • Checks for overexpression or amplification of the HER2 protein
   • Method: IHC/ISH (in situ hybridization) first, then NGS if needed
   • Why it matters: HER2-positive stomach cancers can be treated with targeted therapies like trastuzumab (Herceptin)

2. CLDN18.2 Testing

   • Looks for claudin-18.2 protein on cancer cells
   • Method: IHC or NGS
   • Why it matters: This is an emerging biomarker; newer targeted drugs are being developed against it

3. Next-Generation Sequencing (NGS)

   • Comprehensive genomic profiling that looks at many genes at once
   • Can identify other actionable mutations or alterations
   • When used: Can be considered when limited tissue is available or later in the clinical course

How Testing is Performed

According to NCCN Guidelines:

• Preferred initial approach: IHC/ISH/targeted PCR for single biomarkers
• Tissue source: A biopsy sample from your tumor (obtained during endoscopy)
• If tissue is limited: NGS through a CLIA-approved laboratory can be considered as an alternative
• Liquid biopsy option: If you cannot undergo a traditional biopsy, circulating tumor DNA (ctDNA) testing from blood may be considered for advanced disease

Why This Matters for Your Treatment

These biomarkers help your oncology team:

• Determine which chemotherapy drugs you're likely to respond to
• Identify if you're eligible for targeted therapies or immunotherapy
• Predict how your cancer might behave
• Make personalized treatment recommendations

Questions to Ask Your Healthcare Team

1. Which biomarker tests have been done on my tumor sample?
2. What were the results of my MSI, MMR, PD-L1, HER2, and CLDN18.2 testing?
3. Based on my biomarker results, what treatment options are available to me?
4. If my tissue sample was limited, should we consider NGS testing or liquid biopsy?
5. Will my biomarker results be retested if my cancer progresses or if I develop resistance to treatment?

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This information is for educational purposes only. Always consult your healthcare team for personalized medical advice and decisions.