Abstract Purpose: The intratumoural heterogeneity of human epidermal growth factor receptor
2 (HER2) expression in gastric cancer is a major challenge when identifying patients
who might benefit from HER2-targeting therapy. We investigated the significance of reevaluation
of HER2 status in primary sites and metastatic or recurrent sites in advanced
gastric cancer patients whose primary tumours were initially HER2-negative.