RNA expression profiles of HER2-positive advanced gastric or gastroesophageal junction cancer and healthy gastric mucosa control FFPE samples

A subgroup of patients with HER2-positive metastatic gastric and gastroesophageal junction cancers shows long-term response under trastuzumab maintenance monotherapy. Obviously, HER2 status alone is not able to identify these patients. We performed this study to identify potential new prognostic biomarkers for this long-term responding patient group. Tumor samples of 18 patients with HER2-positive metastatic gastric and gastroesophageal junction cancer who underwent trastuzumab treatment were retrospectively collected from multiple centers. Patients were divided into long-term responding (n=6) or fast-progression group (n=12) according to progression-free survival (PFS≥12 months vs PFS<12 months).We performed microarray-based gene expression analysis to investigate differences in immune cell populations between the patient groups. We retrospectively collected 18 FFPE tumor samples of HER2-positve metastatic or locally advanced gastric or gastroesophageal junction adenocarcinomas (GC/GEJC) prior to trastuzumab treatment and 5 healthy gastric mucosa FFPE samples as control. The patients were divided into long-term responding (PFS>=12, group 1) or fast progressing group (PFS<12, group 2) according to progression-free survival.