e15166 Background: Due to the underlying mechanism of action by inhibiting intracelluar testosterone production and metabolism, the combination of ketoconazole and dutasteride displays a promising treatment option in patients with castrations-resistant prostate cancer (CRPC). The efficacy of this combination has already been shown in a phase-II clinical trial in asymptomatic CRPC patients that reported PSA-response rates of 56% and a biochemical progression free survival of 14.5 months. The aim of our study was to retrospectively analyse the efficacy of the combination in a cohort of patients with CRPC. Methods: Medical records of 26 patients that have been treated with ketoconazole 800mg/d, hydrocortisone 30mg/d and dutasteride 0.5mg/d (K/H/D) between 04/09 and 08/10 have been analyzed. Median age of the patients was 69.94 years with a median PSA of 84.17ng/ml before therapy. Results: 23/26 (88.5%) were eligible for analyzing PSA-response and time to PSA-progression. 7/23 (30.4%) patients experienced a PSA-reduction ≥50% and 5/23 (21.7%) showed even a PSA-reduction of ≥80%. Median time zu PSA-progression of patients with PSA-reduction <50% was 55days compared to 274days (so far) for patients who experienced a PSA-reduction of ≥50% including 5/7 censored patients that did not show PSA-progression at the time of analysis. Updated results of time to progression will be presented at the meeting. Conclusions: Our results confirm the efficacy of the combination of ketoconazole, hydrocortisone and dutasteride in CRPC patients. A subset of patients benefit from treatment by a significant PSA-response leading to long-term PSA progression free survival. Identification of predicitve biomarkers to that helpt to identify patients that are most likely to benefit from treatment seems to be worthwhile.