ERBB2 and breast cancer: In addition, two key observations provide additional rationale for ARIADNE: cyclin-dependent kinase 4/6 inhibitors, highly successful in treating metastatic luminal BC,14 are investigated in the neoadjuvant setting15 and have shown promising results for the treatment of metastatic HER2-positive BC16; and HER2-enriched cancers, a group that comprises approximately 60% of all HER2-positive BCs, are exquisitely sensitive to HER2 blockade.17