Safety and efficacy of maintenance therapy (MT) with a nonspecific cytochrome-P 17 inhibitor (CYP17i) after response/stabilization to docetaxel in metastatic castratation-resistant prostate cancer (mCRPC) patients.
145 Background: ACRPC causes >30,000 deaths/year in the USA. The front-line treatment consists of docetaxel-based chemotherapy (D). 50% of patients (pts) show at least a 50% PSA decline during D and >15% show a partial response (R) in measurable disease. However, most of these pts present progression (P) after a median of 6-8 months (m). mCRPC remains driven by ligand-dependent androgen (A) receptor signaling. Ketoconazole (K) is a nonspecific cytochrome-P 17 inhibitor (CYP17i) able to block adrenal A synthesis. Low-dose K (LDK), (200 mg, t.d.s) has shown interesting activity in mCRPC after P to androgen deprivation therapy (ADT). The FDA recently granted approval to Abiraterone acetate, a selective CYP17i showing a survival benefit after P to D. The role of a CYP17i in the maintenance setting after response/stabilization to D has never been studied. Methods: 38 mCRPC pts starting D after P to ADT maintained LHRHa and additionally received a median of 7 cycles (3-12) of front-line three-weekly D (75 mg/m2) plus daily prednisone (10 mg). 20/38 pts showing no progression to D were enrolled. One month after the last D cycle 10 pts were assigned to MT with LDK plus prednisone (10 mg daily) and continued to receive LHRHa while the 10 pts in the control arm continued on LHRHa alone. Progression-free survival (PFS) was the primary endpoint of the study. Results: After a median follow-up of 27 m, all pts in the control arm progressed after D treatment while 8/10 pts progressed to MT. PFS from D initiation was 11.4 m for MT and 8.9 m for control arm (p=0.025). Toxicity profiles showed no significant differences between both arms. No pts discontinued LDK for toxicity reasons. Conclusions: To our knowledge, this is the first study testing a CYP17i for MT after response/stabilization to D in mCRPC. Although this is a small cohort of pts and a longer follow-up is needed, these preliminary data show a significant benefit in PFS of more than 2 months with LDK MT compared to no MT after D with a favorable toxicity profile. Thus, a further analysis in a larger series and the potential impact of this PFS benefit on the overall survival is warranted.