Clinical implementation of simultaneous multiple biomarkers testing for metastatic or recurrent gastroesophageal adenocarcinoma: a single-institutional experience.

Background: Evaluating multiple biomarkers including human epidermal growth factor receptor 2 (HER2), mismatch repair (MMR) status, programed death-ligand 1 (PD-L1), and claudin 18.2 (CLDN18.2) is essential for selecting appropriate first-line therapy of metastatic gastroesophageal adenocarcinoma (mGEA). However, this can be challenging if tumor tissue amount is limited and may cause delays in the initiation of chemotherapy. Therefore, we assessed the feasibility of multiple biomarkers testing in routine clinical practice. Materials and methods: We reviewed the medical records of treatment-naïve patients with mGEA who underwent prospective multiple biomarkers testing between April 2022 and October 2023 in our institution. Eight biomarker status including HER2, MMR, PD-L1, CLDN18.2, Epstein-Barr virus, fibroblast growth factor receptor 2, epidermal growth factor receptor and mesenchymal epithelial transition expressions were simultaneously examined using biopsy or surgical specimens. Results: A total of 203 patients with mGEA were analyzed. Most patients underwent gastroendoscopy and tumor biopsy shortly after referral to our institution. Biomarkers testing was successfully completed on the first attempt in 198 patients (97.5%). With additional steps including additional biopsy or asking remaining tumor samples from the referring hospital, the biomarker results were eventually available in all cases. The median turnaround time from sample collection to reporting results was 7 days. Consequently, 178 patients (87.7%) could receive first-line treatment after obtaining the biomarker status. Conclusions: Multiple biomarkers testing for patients with mGEA was feasible in clinical practice. Establishment of a testing infrastructure based on the collaboration with multiple departments is essential for implementing biomarker-driven precision treatment.