Adjuvant abemaciclib in early-stage breast cancer: hypothesis-generating safety observations from a real-world cohort study.

Background: Invasive disease-free survival in adjuvant treatment of HR Methods: A retrospective, multi-centre cohort study was conducted in two oncology centres in Pavia, Italy. Patients had to have received at least 3 months of therapy with adjuvant abemaciclib (a CDK4/6 inhibitor). Data on demographics, toxicity, dose reductions and clinical outcomes were analysed. Analyses were descriptive, with continuous variables reported as median (IQR) and categorical variables as counts and percentages. Results: Fifty-four patient records were reviewed (median age 55; six patients ≥70 years (older-age subgroup). Adverse events of any grade were reported in 53/54 patients (98.1%), most commonly haematological and gastrointestinal. Dose reductions occurred more frequently and earlier in the older-age subgroup (66.7% Conclusion: During adjuvant abemaciclib, low-moderate-grade toxicities were common, particularly haematological and gastrointestinal events. Older patients showed a numerically higher rate of dose reductions, suggesting a potential need for personalized dosing and early monitoring in this subgroup. These findings should be considered hypothesis-generating and warrant confirmation in larger prospective studies.