...we present the case of a 69-year-old man with advanced gastric cancer whose tumor was negative for human epidermal growth factor receptor 2 (HER2)...Next-generation sequencing...indicated the presence of the ERBB3 V104L mutation. The patient received irinotecan plus pyrotinib as a third-line therapy and achieved a progression-free survival of 7.6 months with a high quality of life.