NATALEE assessed efficacy and tolerability of 3 years of adjuvant ribociclib plus NSAI compared with a nonsteroidal aromatase inhibitor (NSAI) alone in a broad population of patients with HR+/HER2- early breast cancer, including a select group without nodal involvement. This is the final preplanned analysis of invasive disease-free survival (iDFS).

Premenopausal/postmenopausal women and men were randomized 1:1 to ribociclib (n=2549; 400 mg/day, 3 weeks on/1 week off for 36 months) plus NSAI (letrozole 2.5 mg/day or anastrozole 1 mg/day for 60 months) or NSAI alone (n=2552). Men and premenopausal women also received goserelin (3.6 mg once every 28 days). Patients had anatomical stage IIA (N0 with additional risk factors or N1), IIB, or III disease. The primary endpoint was iDFS. Secondary efficacy endpoints were recurrence-free survival (RFS), distant DFS (DDFS), and overall survival (OS). This final iDFS analysis was planned after ≈500 events.

At data cutoff (21 July 2023), ribociclib was stopped for 1996 patients (78.3%); 1091 (42.8%) completed 3 years of ribociclib, and ribociclib treatment was ongoing for 528 (20.7%). Median follow-up for iDFS was 33.3 months. Overall, 226 and 283 iDFS events occurred with ribociclib plus NSAI vs NSAI alone, respectively. Ribociclib plus NSAI demonstrated significant iDFS benefit over NSAI alone (Hazard Ratio 0.749, 95% Confidence Interval [CI] 0.628-0.892; P=0.0012). The 3-year iDFS rates were 90.7% (95% CI 89.3%-91.8%) vs 87.6% (95% CI 86.1%-88.9%). A consistent benefit was observed across prespecified subgroups, including stage (II/III) and nodal status (+/-). DDFS and RFS favored ribociclib plus NSAI. OS data were immature. No new safety signals were observed.

With longer follow-up and most patients off ribociclib, NATALEE continues to demonstrate iDFS benefit with ribociclib plus NSAI over NSAI alone in the overall population and across key subgroups. Observed adverse events remained stable.