In our research, we assessed the efficacy and toxicity profiles of four platinum and fluoropyrimidine-based doublet chemotherapy regimens in first-line treatment for advanced HER2-negative esophagogastric adenocarcinoma, drawing upon data from the AGAMENON–SEOM national esophagogastric cancer registry. The gene discussed is ERBB2; the disease is gastroesophageal junction adenocarcinoma.