In subgroups analyses, the addition of CDK4/6 inhibitors to ET was associated with significantly prolonged OS compared with the use of ET alone for both pairs of the following 4 patient subgroups: first-line and second-line treatment, premenopausal and postmenopausal women, visceral metastasis and bone-only metastasis, and younger than 65 years and 65 years or older. The gene discussed is CDK4; the disease is bone metastasis.