Clinical Management of Potential Toxicity of Abemaciclib and Approaches to Ensure Treatment Continuation

INTRODUCTION: The association between abemaciclib dose reduction and treatment adherence is not clear. In this study, we examined real-world data of Japanese patients with advanced breast cancer (ABC) to determine how abemaciclib dose reduction is related to treatment continuation. METHODS: This retrospective observational study involved 120 consecutive patients with ABC who received abemaciclib from December 2018 to March 2021. The time to treatment failure (TTF) was estimated using the Kaplan–Meier method. Univariate and multivariate analyses were performed to identify factors associated with a TTF of >365 days (TTF365). RESULTS: According to the dose reduction during treatment, the patients were classified into 100, 200, and 300 mg/day abemaciclib groups. The 300 mg/day group had a TTF of 7.4 months, whereas the 100 and 200 mg/day groups had significantly longer TTFs (17.9 and 17.3 months, respectively; P = 0.0002). In this study, relative to the 300 mg/day arm, TTF was improved in 200mg/day arm and 100 mg/day arm (hazard ratio [HR], 0.55; 95% confidence interval [CI], 0.33–0.93) and [HR], 0.37; 95% CI, 0.19–0.74). For patients who received 300mg/day of abemaciclib dose arm, 200mg/day, and 100mg/day, the median TTF was 7.4 ,17.9 and 17.3 months. The frequently reported adverse effects (AEs) were anemia, increased blood creatinine levels, diarrhea, and neutropenia (90%, 83%, 83%, and 75% of the patients, respectively). Neutropenia, fatigue, and diarrhea were the top AEs causing dose reduction. A multivariate analysis that examined factors associated with achieving TTF 365 confirmed that dose down was an important factor (odds ratio: 3.95, 95% confidence interval: 1.68-9.36, P = 0.002). CONCLUSIONS: In this study, the 100 and 200 mg/day groups had a longer TTF than the 300 mg/day group, and dose reduction was identified as an important factor in achieving longer TTF.