245P Characteristics of real-world (RW) NATALEE and monarchE eligible populations: A US electronic health records (EHR) database analysis

Data from ConcertAI Patient360, a US EHR database (Jan 2015-Jan 2023) was used. Pts ≥18 y with BC diagnosis who had surgery, stage I-III HR+/HER2− EBC at initial diagnosis, and started adjuvant endocrine therapy (ET) were included. NATALEE eligibility was stage II/III disease (AJCC 8th ed) irrespective of lymph node (LN) status, with high recurrence risk criteria for stage IIA T2N0 disease (grade [G] 2 with Ki-67 ≥20% or high genomic risk; G3). monarchE eligibility was ≥4 +LNs (N2/N3) or 1-3 +LNs (N1) and G3 and/or tumor size ≥5 cm (cohort 1) and 1-3 +LNs and Ki-67 ≥20% (G<3 and tumor size <5 cm; cohort 2).

In total, 7060 pts met selection criteria. N0 disease (5286 [74.9%]) was most common, followed by N1 (1388 [19.7%]) and N2/3 (386 [5.5%]). A greater proportion of pts with N0 and N1 disease were eligible for NATALEE than monarchE (Table). T2N0 G2 pts who were eligible for NATALEE were likely undercounted: of 490 T2N0 G2 pts requiring Ki-67/genomic tests to meet NATALEE criteria, only 248 (50.6%) had a reported result, of whom 112 met the increased-risk criteria. Overall, 30.6% pts were eligible for NATALEE vs 14.5% for monarchE. Median age was 60 vs 59 y, respectively; 21.5% vs 22.8% were premenopausal, 55.6% vs 67.5% had prior chemotherapy (CT). For pts with N0 disease eligible for NATALEE: median age, 60 y; premenopausal, 20.3%; prior CT, 48.9%.

This RW analysis indicates that NATALEE represents a much larger number of pts at increased risk of recurrence who may benefit from addition of a CDK4/6i to ET vs monarchE, including select pts with N0 and all pts with macroscopic N1 disease.