A multicenter phase I study of cabazitaxel (Cbz), mitoxantrone (Mito), and prednisone (Pred) (CAMP) for chemotherapy-naive patients with metastatic castration-resistant prostate cancer (mCRPC).

Abstract

243 Background: Cbz/pred extends survival in mCRPC patients (pts) following docetaxel and first-line studies comparing Cbz to docetaxel are ongoing. Mito/pred also has anti-tumor activity in mCRPC and a non-overlapping mechanism of action and toxicity profile with Cbz. A multicenter phase I trial was initiated through the DOD PCCTC to establish the maximally tolerated dose (MTD) of the combination of Cbz, Mito, and Pred. Methods: Chemotherapy (chemo)-naive pts with mCRPC were enrolled in an accelerated titration design. The primary objective was to determine the MTD of CAMP; secondary objectives included assessing PSA and objective response rates and duration of response. Starting dose of Cbz was 25 mg/m2 (the currently approved single-agent dose) and Mito 4 mg/m2, administered on day 1 of a 21-day cycle. Mito was escalated by 2 mg/m2 per dose level. Pred 5 mg BID and pegfilgrastim were administered with each cycle. Results: 9 pts were enrolled (dose level I, N = 1; dose level II, N = 1; dose level III, N = 3; dose level IV N = 4). The median age was 67 (range 55-81) and the median baseline PSA was 82.3 (range 20.4-791.2). There were 2 DLTs observed at dose level IV (Cbz 25 mg/m2 + mito 10 mg/m2), both grade 4 sepsis. The most common grade 3 adverse events were hematologic (neutropenia, n = 5; febrile neutropenia, n = 2, thrombocytopenia, n = 2). 6 of 9 pts remain on study (range 2.2 - 10.5+ months). Maximal PSA declines from baseline > 50% have been observed in 4/7 (57%) evaluable pts to date. 2 of 4 pts with measurable disease have experienced partial responses and a third has had a minor response after 4 cycles of chemo. The median progression-free survival and duration of response have not been reached. Conclusions: The approved single-agent dosage of Mito (12 mg/m2) could not be safely reached in combination with Cbz 25 mg/m2. Pre-planned evaluation of an alternate dosing strategy combining Mito with Cbz 20 mg/m2, which has demonstrated activity in mCRPC and potentially less hematologic toxicity, is underway. Preliminary efficacy data are encouraging but additional follow-up and further study of the treatment combination is required. Clinical trial information: NCT01594918.