Analysis of Risk Factors for Abemaciclib-Induced Diarrhea

Diarrhea is the most common adverse event associated with abemaciclib, a CDK4/6 inhibitor for HR+/HER2 breast cancer. Data on risk factors in Japanese patients are limited; thus, this study aimed to identify them. We retrospectively analyzed data from 75 Japanese patients who received abemaciclib between May 2019 and June 2025. Risk factors for Grade ≥ 2 diarrhea within 56 days of initiation were identified using multivariate logistic regression and Cox proportional hazards models. Sensitivity analysis was also performed to evaluate the impact of short observation periods. Grade ≥ 2 diarrhea occurred in 18 patients (24.0％). In the multivariate logistic regression, a history of three or more prior chemotherapy regimens (Adjusted Odds Ratio [aOR]; 13.70, 95％ Confidence Interval [CI]; 1.710 – 109.000, P = 0.014) and a starting dose of 300 mg (aOR; 18.80, 95％CI; 1.780 – 199.000, P = 0.015) were identified as independent risk factors. Cox regression analysis also confirmed these two factors as independent predictors of early onset. Although the initial analysis suggested a protective effect of concomitant probiotics, this association lost significance in a sensitivity analysis excluding patients with short observation periods. These findings indicate that risk assessment should prioritize detailed treatment history and dose to enable individualized management strategies.