Four Validated Biomarkers Now Guide Advanced Esophageal Cancer Treatment
Four biomarkers—MMR, HER2, PD-L1, and Claudin 18.2—are now validated for advanced esophageal cancer, guiding immunotherapy and targeted treatment decisions. Checkpoint inhibitors show clear benefit in MSI-H and PD-L1-positive subgroups, with long-term survival observed. NCCN guidelines recommend broad testing to personalize therapy.
Advanced esophageal cancer now has four validated biomarkers — MMR, HER2, PD-L1, and Claudin 18.2 — that should be tested in all patients with advanced disease, according to recent guidance discussed at an American Society of Clinical Oncology meeting.
The markers, all detectable by immunohistochemistry, have been incorporated into the National Comprehensive Cancer Network (NCCN) recommendations. The 2026 update emphasizes testing for microsatellite instability-high (MSI-H) or deficient mismatch repair, a subgroup representing 3-5% of advanced gastroesophageal adenocarcinomas. These patients are notoriously chemoresistant, but phase III trials such as KEYNOTE-062 and CheckMate 649 have demonstrated a clear advantage for immune checkpoint inhibitors like pembrolizumab and nivolumab over chemotherapy.
PD-L1 testing by combined positive score (CPS) is also critical. Trials including RATIONALE-305, KEYNOTE-859, and CheckMate 649 show consistent benefits in progression-free and overall survival for patients with CPS ≥1, with 15-20% of those with high PD-L1 expression becoming long-term survivors.
For unresectable or metastatic disease, HER2 immunohistochemistry and Claudin 18.2 testing are additionally recommended, the latter following FDA approval of zolbetuximab. Next-generation sequencing may be considered to identify rare BRAF or NTRK alterations that qualify patients for tumor-agnostic approved checkpoint inhibitors.
In the perioperative setting, the focus is shifting to immunotherapy. The NCCN highlights that MSI-H patients may not benefit from neoadjuvant chemotherapy but could respond to neoadjuvant immune checkpoint inhibitors. Questions persist about the necessity of adding chemotherapy or using dual checkpoint inhibition for these patients.
Biomarker discovery for resectable disease remains ongoing, and genomic biomarkers are under investigation in advanced disease but have yet to be validated in phase III trials. For patients whose disease progresses after immunotherapy, the role of chemotherapy versus targeting other pathways is being evaluated, especially in cases of oligometastatic progression.