Although most patients were enrolled after 2018, when the SOFT and TEXT trials (NCT00066690, NCT00066703) established the efficacy of OFS combined with ET in premenopausal HR+ BC, the FLEX registry captures limited data on the use of OFS and CDK4/6 inhibitors, both of which now represent standard treatment for early-stage BC. This evidence concerns the gene CDK4 and breast cancer.