Adjuvant abemaciclib outcomes in routine clinical practice (experience of several Moscow centers).

Abstract

e12522 Background: Adjuvant abemaciclib (aA) combined with endocrine therapy (ET) is one of standard treatment for HR+/HER2- early breast cancer (BC). While efficacy has been established in MonarchE clinical trial, comprehensive real-world evidence of abemaciclib effectiveness, especially in high-risk populations with early BC, remains limited. This multicenter observational study evaluated aA outcomes in routine clinical practice. Methods: This retrospective analysis included 160 HR+/HER2- breast cancer patients receiving A with ET across multiple centers in Moscow. Primary endpoint was invasive disease-free survival (iDFS). Secondary endpoints included safety, treatment duration, and reasons for discontinuation. Survival estimates were calculated using Kaplan-Meier methodology. Data cutoff was December 2024, with median follow-up of 21.0 months (range 5.5-46.1). Results: Median age was 50 years (range 27-74); 46.3% patients were premenopausal. Disease stage distribution included Stage II (40%), and Stage III (60%). Among Stage III patients (n=96), 45% had T4 disease and 39.4% had N3 nodal involvement. Most patients (81.2%) presented with high-risk features: Ki-67>20%, grade 3 (37.4%), lymph node involvement (83.1%). Prior treatment included neoadjuvant chemotherapy in 62.5% and adjuvant in 37.5% of patients, with 88.1% receiving anthracycline-taxane combinations. At baseline, 89.4% received aromatase inhibitors, 10% switched from tamoxifen to aromatase inhibitors, and 0.6% continued tamoxifen as ET partner. Seven progression events (4.4%) were documented during follow-up. The iDFS rates were 99.4%, 96.2%, and 95.6% at 12, 24, and 36 months, respectively. Median time to progression in patients with disease recurrence was 17.7 months (range 6.1-29.8). At data cutoff, 101 patients (63.1%) continued treatment, 29 (18.1%) completed planned therapy duration. Main reasons for discontinuation included toxicity (n=13, 8.1%), disease progression (n=7, 4.4%), treatment refusal (n=7, 4.4%) and other reasons (n=3, 1.9%). Most common adverse events were neutropenia (13.8%, including Gr. 3 in 5%) and diarrhea (10.6%, predominantly Gr. 1-2). Dose reductions were required in 22% of patients. Conclusions: In this real-world cohort of HR+/HER2- with locally advanced BC disease and high-risk features, abemaciclib demonstrated favorable efficacy with 12, 24 and 36 months iDFS rates comparable to MonarchE despite more unfavorable patient characteristics. Safety profile was manageable through dose modifications, with most patients maintaining long-term treatment. These results support adjuvant abemaciclib's effectiveness in routine clinical practice, particularly in high-risk patient populations.