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PubMed This is a summary of 22 peer-reviewed journal articles Updated
Medical Oncology · Esophageal Cancer

What Biomarkers Should Be Tested in Esophageal Cancer?

At a Glance

In advanced esophageal cancer, biomarker testing commonly includes HER2, PD-L1 with a CPS score, dMMR/MSI, and TMB. For HER2-negative adenocarcinoma at the gastroesophageal junction, CLDN18.2 testing and broad NGS may identify additional treatment or trial options.

When you are diagnosed with advanced esophageal cancer (meaning the cancer is recurrent, cannot be removed by surgery, or has spread to other parts of the body), analyzing the tumor’s specific characteristics is a critical step in care [1]. Besides standard markers like HER2 and PD-L1, it is important to ask your doctor about testing for Mismatch Repair (dMMR) / Microsatellite Instability (MSI), Tumor Mutational Burden (TMB), and, in specific cases, newer targets like Claudin 18.2 (CLDN18.2).

Knowing your tumor’s profile helps your care team determine if adding a targeted therapy or immunotherapy to traditional chemotherapy could be beneficial for you. Biomarker testing is complex and involves different types of laboratory tests; some look at proteins on the surface of cells, while others look deep into the tumor’s DNA and RNA.

Protein Staining Tests (IHC and ISH)

Many of the most important biomarkers in esophageal cancer are proteins. Pathologists usually test for these using a technique called Immunohistochemistry (IHC), sometimes combined with In Situ Hybridization (ISH) to confirm the results.

  • HER2: This is a protein that can promote the growth of cancer cells. Testing is particularly important if you have esophageal or gastroesophageal junction (GEJ) adenocarcinoma, as about 20% of advanced gastric and GEJ adenocarcinomas overexpress this protein [1][2]. If an IHC test (and ISH confirmation, if needed) shows the tumor is HER2-positive, your doctor may recommend a treatment plan that combines standard chemotherapy with a HER2-targeted medication [1][3].
  • PD-L1: PD-L1 is a protein that helps cancers hide from your immune system. This test is relevant for both squamous cell carcinoma and adenocarcinoma [4][5]. It is measured using a Combined Positive Score (CPS), which counts PD-L1 expression on both tumor cells and surrounding immune cells [4]. A higher CPS indicates the tumor may be more likely to respond to certain immunotherapy drugs (like pembrolizumab), though it does not guarantee a response, and the exact threshold for treatment varies by drug and region [4][6].
  • Mismatch Repair (dMMR) / MSI-H: This tests for the cancer’s inability to properly repair mistakes made when DNA is copied. Found in a small percentage of esophageal cancers, dMMR (tested via IHC) or MSI-H (tested via PCR or sequencing) are markers that often predict a strong response to immune checkpoint inhibitors [7][8]. Finding dMMR/MSI-H can open up specific immunotherapy options and may also prompt your doctor to recommend genetic counseling, as it can sometimes be linked to inherited conditions like Lynch syndrome [7][9].
  • Claudin 18.2 (CLDN18.2): This is a newer protein target. Recently, a targeted therapy (zolbetuximab) was approved in certain regions for patients with HER2-negative, locally advanced unresectable or metastatic adenocarcinoma of the stomach or gastroesophageal junction (GEJ) [10][11]. Eligibility requires a specific validated IHC test showing moderate-to-strong membranous staining in at least 75% of tumor cells [10][12]. It is not currently a blanket approval for primary esophageal cancer, but if your tumor is an adenocarcinoma located near the stomach (the GEJ), this is an important test to discuss [11][13].

Genomic Sequencing (NGS)

While IHC looks at proteins, Comprehensive Genomic Profiling (CGP) or Next-Generation Sequencing (NGS) looks at the tumor’s DNA and RNA. NGS complements, but does not replace, protein tests like PD-L1 or HER2 IHC.

  • Tumor Mutational Burden (TMB): Usually measured by NGS, TMB counts the number of mutations per megabase of tumor DNA. Tumors with a high number of mutations (TMB-high) might be more easily recognized by the immune system [14][15]. In some regions, a TMB-high result can make a patient eligible for tissue-agnostic immunotherapy, typically if prior treatments have failed and there are no satisfactory alternatives [14][15].
  • Broad NGS Panels: A broad panel can test hundreds of genes at once [16][17]. It may discover rare but actionable changes—such as EGFR amplifications or NTRK/RET fusions—which might qualify you for specific clinical trials or off-label treatments [18][19]. However, it can also return “variants of uncertain significance” (mutations that don’t yet have a known treatment) or occasionally flag a potential inherited mutation that requires separate germline testing [18][19].

The Testing Process and Biopsies

Testing can often be done on tissue from an initial biopsy or surgery. If that tissue is too small or too old, a new biopsy may be considered by your oncology team [20][21]. In some cases, a “liquid biopsy” (a blood test looking for tumor DNA) might be used, though a negative liquid biopsy often still requires confirmation with a tissue sample [22][20]. Remember that finding a biomarker does not guarantee a cure or a perfect treatment, but it gives your oncology team the clearest evidence available for navigating your therapy choices.

Common questions in this guide

Which biomarker tests are usually recommended for advanced esophageal cancer?
Testing commonly includes HER2, PD-L1 reported as a Combined Positive Score, and mismatch repair or microsatellite instability testing. Tumor mutational burden and broad next-generation sequencing may add useful information, while CLDN18.2 is most relevant in selected HER2-negative adenocarcinomas involving the gastroesophageal junction. The exact testing plan depends on the cancer type, location, prior treatment, and local treatment approvals.
What can HER2 and PD-L1 results tell me?
A HER2-positive result may support adding a HER2-targeted medicine to chemotherapy, especially for adenocarcinoma of the esophagus or gastroesophageal junction. A PD-L1 result is reported as a Combined Positive Score and may help determine whether immunotherapy is appropriate for squamous cell carcinoma or adenocarcinoma. Neither result guarantees that a treatment will work.
How do dMMR, MSI-H, and TMB results affect treatment?
dMMR or MSI-H means the tumor has difficulty repairing DNA-copying errors, and these tumors may respond well to immune checkpoint inhibitors. The result can also lead to a discussion about genetic counseling because it may sometimes be associated with an inherited condition such as Lynch syndrome. A TMB-high result may support tissue-agnostic immunotherapy in some regions and treatment settings, but it does not guarantee a response.
When is CLDN18.2 testing useful for esophageal cancer?
CLDN18.2 testing is most worth discussing when the cancer is a HER2-negative adenocarcinoma at or near the gastroesophageal junction. In certain regions, treatment eligibility requires a validated protein test showing the required level of CLDN18.2 on tumor cells. It is not a routine treatment marker for every primary esophageal cancer.
Could broad NGS testing find another treatment option?
Broad next-generation sequencing examines many tumor genes at once and may identify uncommon changes, such as NTRK or RET fusions, that could support a clinical trial or another targeted treatment discussion. It can also find changes whose meaning is not yet known, called variants of uncertain significance. A possible inherited finding may require separate germline testing and genetic counseling.
Can my old biopsy or a blood test provide enough tissue for biomarker testing?
Testing can often use tissue from an earlier biopsy or surgery, but a new biopsy may be needed if the sample is too small or old. A liquid biopsy can sometimes look for tumor DNA in blood, but a negative blood result often needs confirmation with tissue testing. Your oncology team can determine which sample is most reliable for the tests being considered.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Is my tumor an adenocarcinoma or squamous cell carcinoma, and is it located at the gastroesophageal junction?
  2. 2.Has my tumor tissue been tested for HER2, PD-L1 (with a CPS score), and mismatch repair (dMMR/MSI)?
  3. 3.Based on my tumor's location and HER2 status, am I a candidate for Claudin 18.2 testing?
  4. 4.Would Comprehensive Genomic Profiling (NGS) be appropriate for me to look for rare mutations or clinical trial options?
  5. 5.Do we have enough tissue from my previous biopsy to run these tests, or will I need a new tissue or liquid biopsy?

Questions For You

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Related questions

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References

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This page explains biomarker testing for advanced esophageal cancer for informational purposes only and does not replace medical advice. Your oncology and pathology teams can interpret your results and recommend appropriate next steps.

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