iCDK4/6	Cyclin-dependent kinase 4 and 6
HER-2	Human epidermal growth factor receptor 2
ER	Estrogen receptor
PR	Progesterone receptor
Ki67	Proliferation index
RB	Retinoblastoma protein
E2F	Transcription factor for DNA replication
CDK	Cyclin-dependent kinase
HR	Hazard ratio
NSAI	Non-steroidal aromatase inhibitor
AI	Aromatase inhibitor
CI	Confidence interval
OS	Overall survival
PFS	Progression-free survival