ERBB2 and gastric cancer: HER2 amplification and overexpression have been observed in various types of cancers, including but not limited to breast cancer, gastric cancer, non-small cell lung cancer (NSCLC), bile duct cancer, bladder cancer, and colorectal cancer [9–13]. This association may indicate an unfavorable prognosis or the development of drug resistance in the treatment of various malignancies [14].