In summary, zanidatamab treatment reduced total HER2, pHER3, and pAKT levels in HER2-expressing SK-BR-3 and JIMT-1 breast cancer cells, and reduced HER2, pHER2, pHER3 pEGFR, pAKT and pERK in NCI-N87 gastric cancer cells. Here, ERBB2 is linked to breast cancer.