Combination of carboplatin (AUC4) and cabazitaxel (25 mg/m2) in mCRPC patients not or no longer responding to cabazitaxel monotherapy

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Background: Cabazitaxel monotherapy is a second line treatment option for mCRPC patients. However, not all patients have a PSA response on this treatment, while a proportion of patients develop resistance during cabazitaxel treatment. Platinum drugs might be effective in poorly differentiated disease. Ongoing trials suggest effectivity of the combination in mCRPC, however, thus far clinical parameters cannot predict a response. Therefore, we investigated the addition of carboplatin to cabazitaxel in mCRPC patients who do not have a psa response on cabazitaxel monotherapy or have a PSA rise during treatment. Methods: 19 patients (WHO PS ≤2) who were not responding to ≥2 cycles cabazitaxel monotherapy (25 mg/m2) or two rises of PSA during cabazitaxel were included in this prospective cohort study. All patients received the combination of carboplatin (AUC 4) and cabazitaxel (25 mg/m2). Previous therapies, PSA response, WHO performance score, Progression Free Survival (PFS), Overall Survival (OS) and adverse events were monitored. Results: Median age was 66.7 years, 21% of patients had a WHO PS of 2, 68% had a Gleason score ≥8, 74% had bone metastases, 63% lymph node metastases and 26% visceral metastases. All patients received docetaxel prior to cabazitaxel, 6 patients (31,6%) received abiraterone and 15 patients (78,9%) enzalutamide. Combination therapy was initiated after a median of 4.1 cycles monotherapy [IQR 3.0-6.0]. Patients were treated with a median of 3.8 [IQR 2.8-6.3] cycles of combination therapy. Eight patients (42,2%) had a PSA decrease of > 25% and 4 patients (21,1%) had a PSA decrease of ≥50%. One patient had a WHO PS improvement of 2. Median PFS was 8.1 [IQR 6.0-15.1] months and median OS 13.0 months. Anemia was the most common adverse event (≥ grade 2) during combination therapy (62%), while thrombopenia was only found in one patient (5%). Other common adverse events were fatigue (43%), nausea (24%), pain (33%) and constipation (10%). Conclusions: Our data suggests that combination treatment of cabazitaxel and carboplatin might be effective in heavily pretreated patients not, or no longer responding to cabazitaxel monotherapy.