Results of a phase II study of sunitinib (SU) maintenance after response to docetaxel in metastatic castration-resistant prostate cancer (mCRPC).

153 Background: Docetaxel (D) remains the standard first cytotoxic therapy in mCRPC. Given its mechanism of action, acceptable toxicity profile and simple administration, SU had potential as maintenance therapy for mCRPC. In this multicenter study, we evaluated the tolerability and efficacy of SU monotherapy in patients (pts) with mCRPC who have responded to D. Methods: Pts withmCRPC and responding/stable disease at the time of D completion were enrolled in this multicentre trial. Pts received 50mg of SU daily on 4/2 week on/off cycles. The primary endpoint was progression-free survival (PFS), defined on the basis of RECIST criteria and worsening disease-related symptoms requiring further therapy. Because the effect of SU on PSA is not well known, PSA progression alone was not considered disease progression. PFS of 180 days was considered to be a clinically meaningful threshold for recommending further study of SU. PSA response was a secondary endpoint. The threshold for PSA-progression (PSA-P) was defined as a 25% increase in PSA over baseline. Results: Twenty-three pts were enrolled and treated. Mean age was 66.5 years (48-78). ECOG scores of 0, 1, and 2 were reported for 9, 13 and 1 pts respectively. Mean number of prior cycles of D was 8.6 (4-12). A total of 92 cycles of SU were administered; a mean of 4 per pt (1-11). Mean follow-up was 5.4 months (0.6-15). A total of 479 adverse events (AE) were recorded, of which 88% were Grade 1-2 and 12% were Grade 3-4. The AE were of a type and severity expected for SU. Three Grade 4s occurred, consisting of hepatitis, myelosuppression, and pneumonia. Median PFS was 133 days (95% CI: 48-154). Most pts had immediate PSA increases without evidence of disease progression, with the mean increases in PSA over baseline being 197%, 342%, and 1437% in Cycles 1, 2, and 3, respectively (p<0.05). Conclusions: Although SU was well tolerated as maintenance therapy with predictable side-effects, median PFS was lower than the predefined threshold of 180 days. PSA values were not informative as significant increases were observed as early as Cycle 2. This agent is not considered worthy of further investigation in this setting of maintenance therapy. Clinical trial information: NCT00550810.

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