ERBB2 and breast cancer: Over the course of treatment, not only do the breast cancer cells adapt to estrogen deprivation and develop resistance to chemotherapy via multidrug resistance‐associated proteins as well as the antiapoptotic mechanisms, but proteins associated with the PAM pathway also contribute to the resistance to CDK4/6 inhibitors and anti‐HER2 treatment [5, 6, 7, 11, 12].