The addition of CDK4/6 inhibitors to ET (letrozole or fulvestrant) significantly reduced mortality risk by 20% in younger patients (fixed-effect model; HR 0.80; 95% CI 0.72–0.9; p < 0.01) and 21% in older BC patients (HR 0.79; 95% CI 0.69–0.91; p < 0.01). The gene discussed is CDK4; the disease is breast cancer.