In terms of all grade adverse events, CDK4/6 inhibitors plus endocrine therapy group showed significantly higher rates of neutropenia (risk ratio [RR]=14.77, 95% CI=10.26-21.26), nausea (RR=1.66,95% CI=1.49-1.85), fatigue (RR=1.22, 95% CI=1.02-1.45), diarrhoea (RR=1.64, 95% CI=1.08-2.48), leucopenia (RR=9.95, 95% CI=7.43-13.32), vomiting (RR=1.74, 95% CI=1.29-2.34), anaemia (RR=3.53, 95% CI=2.36-5.26) (Table 3). Here, CDK4 is linked to neutropenia.