While significantly improving PFS and OS over endocrine therapy alone, ribociclib plus endocrine therapy for pre/perimenopausal women with HR+/HER2- advanced breast cancer is not cost-effective with an ICER of $282,996/QALY, despite assuming a generous WTP threshold of $150,000/QALY for the U.S. healthcare setting. Here, ERBB2 is linked to breast carcinoma.