To improve therapeutic outcome of the endocrine therapy, other agents with different mechanisms have been investigated: pan-class I phosphatidylinositol 3-kinase (PI3K) inhibitors (e.g. alpelisib and buparlisib),3,4 mammalian target of rapamycin (mTOR) inhibitors (e.g. everolimus),5,6 and cyclin-dependent kinase CDK4 and CDK6 inhibitors (e.g. palbociclib and ribociclib).7–9 For the treatment of ERBB2-positive breast cancer, PI3K and mTOR inhibitors are used together with ERBB2-targeted antibodies. This evidence concerns the gene ERBB2 and breast cancer.