ERBB2 and cancer: An important, but yet to be elucidated connection is between the HER2 pathway and the immune checkpoint pathway; PD-L1 gene can be activated to produce PD-L1 to inhibit the TILs thereby impairing their ability to kill cancer cells and also reducing the effectiveness of anti-HER2 monoclonal antibodies including pertuzumab, ADC, and BsAB.