[Risk Factors for Dose Reduction in Patients Receiving Abemaciclib-A Multicenter Retrospective Study]

Abemaciclib is a cyclin-dependent kinase 4/6 inhibitor that has been shown to be effective in the treatment of hormone receptor-positive and HER2-negative breast cancer. On the other hand, diarrhea, impairment of liver function, interstitial lung disease, and hematologic toxicity have been reported as adverse events. Those dose reductions lead to a decrease in treatment intensity and may affect prognosis. Therefore, we conducted a survey to identify risk factors for patients whose dose is reduced after abemaciclib administration due to side effects. Breast cancer patients who received abemaciclib at study participating centers between December 2018 and December 2022 were included. The abemaciclib standard dose and dose reduction groups were studied retrospectively, and logistic regression analysis was performed to examine risk factors associated with dose reduction. There were 73 patients with a median age of 61 years, and 35 patients(47.9%)underwent dose reduction. The most common reason for dose reduction was diarrhea, followed by neutropenia. Multivariate analysis showed significant differences in 2 factors: age≥65 years(odds ratio: 4.84, 95%CI: 1.55-15.10, p=0.007)and neutrophil count<3,660/μL before starting treatment(odds ratio: 5.24, 95%CI: 1.58-17.40, p=0.007). This study suggested that age 65 years or older and a neutrophil count of 3,660/μL or lower before treatment initiation may be risk factors for dose reduction after starting abemaciclib. The effect of dose reduction on treatment efficacy and its relationship to the duration of treatment should also be studied in the future.