ERBB2 and gastric cancer: Anti‐PD1/PD‐L1 antibody plus human epidermal growth factor receptor 2 (HER2) antibody and chemotherapy have become the new first‐line therapy for HER2 overexpression‐positive advanced gastric cancers (GC), suggesting that HER2 and PD‐L1 play a vital role in guiding systemic treatment for patients with GC.