Decoding NATALEE and MonarchE eligibility criteria in a real-world cohort of early breast cancer patients.

The NATALEE trial expanded the use of adjuvant cyclin-dependent kinase 4/6 inhibitors beyond the MonarchE trial's criteria for early breast cancer (eBC). We conducted a retrospective analysis comparing a large real-world (RW) cohort of 762 consecutive eBC patients with those enrolled in the NATALEE and MonarchE randomized controlled trials (RCTs) to evaluate differences in eligibility. Our analysis revealed that 41.7% of RW patients met NATALEE's eligibility criteria, significantly more than the 21.8% who met MonarchE's criteria, reflecting NATALEE's broader indication. Real-world patients were older, had less advanced tumors, and were less likely to be treated with adjuvant chemotherapy compared to the RCT populations. None of the RW patients was deemed eligible for ribociclib based solely on high genomic risk. These findings underscore significant differences in clinical characteristics and potential treatment eligibility, highlighting the need for critical assessment of RCTs results in clinical practice.