ERBB2 and breast cancer: As for ribociclib, in a phase III RCT that compared the addition of ribociclib to AI versus AI monotherapy in the first-line treatment of HR+/HER-2 stage IV breast cancer women who are postmenopausal, the former comparator had a longer PFS duration of 19.3 months (to not reached during the observational study period) versus 14.7 months in the AI group (20).