Due to the in vitro anti-tumor efficacy of the novel isolated PD-L1_1 mAb and to its ability to recognize with high affinity and specificity PD-L1 also on breast cancer cells, inhibiting cell growth and affecting the downstream MAPK pathways, we investigated the possibility to use it in combination with the anti-ErbB2 compact antibody, Erb-hcAb, capable of inhibiting breast tumor cell growth in vitro and in vivo21,24,37. The gene discussed is ESR2; the disease is breast cancer.