The increment of tumor-infiltrating dendritic cells and CD8+ T cells, the augmentation of major-histocompatibility-complex (MHC) class I in cancer cells, and the rejection of rechallenged cancer cells by adaptive immune T cells were observed in an immunocompetent mouse model with human HER2-expressing murine colorectal cancer (CRC) cells, which might a reason for a superior anti-tumor effect of T-DXd as compared with trastuzumab alone and T-DM1. The gene discussed is ERBB2; the disease is cancer.