Importance Many patients 65 years or older with metastatic castration-resistant prostate cancer (mCRPC) are denied taxane chemotherapy because this treatment is considered unsuitable.Objective To determine whether biweekly cabazitaxel (CBZ), 16 mg/m(2) (biweekly CBZ16), plus prophylactic granulocyte colony-stimulating factor (G-CSF) at each cycle reduces the risk of grade 3 or higher neutropenia and/or neutropenic complications (eg, febrile neutropenia, neutropenic infection, or sepsis) compared with triweekly CBZ, 25 mg/m(2) (triweekly CBZ25), plus G-CSF (standard regimen).Design, Setting, and Participants A total of 196 patients 65 years or older with progressive mCRPC were enrolled in this prospective phase 3 randomized clinical trial conducted in France (18 centers) and Germany (7 centers) between May 5, 2017, and January 7, 2021. All patients had received docetaxel and at least 1 novel androgen receptor-targeted agent.Interventions Patients were randomly assigned 1:1 to receive biweekly CBZ16 plus G-CSF and daily prednisolone (experimental group) or triweekly CBZ25 plus G-CSF and daily prednisolone (control group).Main Outcome and Measures The primary end point was the occurrence of grade 3 or higher neutropenia measured at nadir and/or neutropenic complications.Results Among 196 patients (97 in the triweekly CBZ25 group and 99 in the biweekly CBZ16 group), the median (IQR) age was 74.6 (70.4-79.3) years, and 181 (92.3%) had an Eastern Cooperative Oncology Group performance status of 0 or 1. The median (IQR) follow-up duration was 31.3 (22.5-37.5) months. Relative dose intensities were comparable between groups (median [IQR], 92.7% [83.7%-98.9%] in the triweekly CBZ25 group vs 92.8% [87.0%-98.9%] in the biweekly CBZ16 group). The rate of grade 3 or higher neutropenia and/or neutropenic complications was significantly higher with triweekly CBZ25 vs biweekly CBZ16 (60 of 96 [62.5%] vs 5 of 98 [5.1%]; odds ratio, 0.03; 95% CI, 0.01-0.08; P < .001). Grade 3 or higher adverse events were more common with triweekly CBZ25 (70 of 96 [72.9%]) vs biweekly CBZ16 (55 of 98 [56.1%]). One patient (triweekly CBZ25 group) died of a neutropenic complication.Conclusions and Relevance In this randomized clinical trial, compared with the standard regimen, biweekly CBZ16 plus G-CSF significantly reduced by 12-fold the occurrence of grade 3 or higher neutropenia and/or neutropenic complications, with comparable clinical outcomes. The findings suggest that biweekly CBZ16 regimen should be offered to patients 65 years or older with mCRPC for whom the standard regimen is unsuitable.
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