ESR2 and breast neoplasm: Finally, to verify whether combinatorial treatments of anti-ErbB2 and anti-PD-L1 antibodies can potentiate their antitumor effects, PD-L1_1 and an anti-ErbB2 compact antibody (Erb-hcAb) capable of inhibiting breast tumor growth, previously developed in our laboratory21–24, have been tested in combination to evaluate by cytotoxic assays their effects on tumor growth in comparison with the single treatments.