Adjuvant abemaciclib in pN2-3 patients with HR+/HER2− early breast cancer: Real-world outcomes from Moscow centers.

Abstract

e12535 Background: Adjuvant abemaciclib (adA) plus endocrine therapy (ET) resulted in a statistically and clinically significant improvement in invasive disease-free survival (iDFS) and overall survival (OS) compared with ET alone in patients with high-risk HR+ HER2- early breast cancer (BC). Although efficacy was established in the monarchE trial, real-world evidence, particularly in high-risk subgroups such as node-positive (pN2-3) disease, remains limited. This multicenter observational study assessed adA outcomes in routine practice. Herein, we present an updated analysis of the pN2-3 subgroup, associated with the poorest prognosis. Methods: This retrospective analysis included 160 patients with HR+/HER2- BC receiving adA plus ET across Moscow centers, of whom 135 had pN2-3 disease. The primary endpoint was iDFS. Secondary endpoints included safety, treatment duration, and discontinuation reasons. Data cutoff was November 2025 (median follow-up, 24.0 months). Results: Median age was 51.6 years (range, 27-74); 44.4% were premenopausal. Histologic subtypes included lobular (15.6%; n = 21), invasive ductal/non-specific (77.0%; n = 104), and other (7.4%; n = 10). Tumor grades were G1 (5.2%), G2 (62.2%), and G3 (32.6%). Prior chemotherapy comprised neoadjuvant (60.7%) and adjuvant (39.3%) regimens. Baseline ET included aromatase inhibitors (89.6%), switch from tamoxifen to aromatase inhibitors (9.6%), and tamoxifen continuation (0.8%). Eight progression events (5.9%) occurred: locoregional recurrence (n = 2) and distant metastases (n = 6). iDFS rates were 100.0%, 94.7%, and 93.5% at 12, 24, and 36 months, respectively. At cutoff, 55 patients (40.7%) continued treatment and 49 (36.3%) completed planned duration. Discontinuations were due to toxicity (n = 14; 10.4%), progression (n = 8; 5.9%), patient refusal (n = 7; 5.2%), and other (n = 2; 1.5%). Among toxicity-related discontinuations, neutropenia ≥G2 occurred in 5, G3 anemia in 1, G1-2 diarrhea in 5, and G2 rash in 2. Conclusions: In this high-risk pN2-3 cohort with HR+/HER2- early BC, adjuvant abemaciclib yielded favorable real-world efficacy, with iDFS rates of 100.0%, 94.7%, and 93.5% at 12, 24, and 36 months. The safety profile was manageable via dose adjustments, enabling long-term treatment in most patients. These findings affirm abemaciclib's role in routine high-risk settings.