Thus, the anti-ErbB2 antibody, Erb-hcAb, was combined with PD-L1_1 mAb for the treatment of ErbB2-positive breast cancer cells, showing that the combinatorial treatment inhibits the growth of tumor cells more efficiently than when they are used as single agents on different tumor cell lines, including the aggressive Trastuzumab-resistant JIMT-1 cells. The gene discussed is ESR2; the disease is breast cancer.