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Suppression of gonadal androgens by medical or surgical castration remains the mainstay of treatment for patients with advanced prostate cancer. However, the response to treatment is not durable, and transition to a “castration-resistant” state is invariable. Recent advances in our understanding of the androgen receptor signaling pathway have led to the development of therapeutic strategies to overcome castration resistance. This article reviews current concepts and challenges behind targeting continued androgen receptor signaling in castration-resistant prostate cancer and provides an overview of recently completed and ongoing clinical trials of novel hormonal agents, with a focus on abiraterone acetate and enzalutamide (MDV3100).

Multiple survival-prolonging treatments have now been established in castration-resistant prostate cancer (CRPC) and molecular analyses have identified further potential therapeutic targets. Optimizing the clinical development of novel anticancer drugs therefore remains an urgent priority in CRPC. In this chapter we will review issues specific to conducting Phase I and II clinical trials of targeted therapies for men with CRPC, including: trial design; selection of trial participants; safety and efficacy monitoring in trial participants; and the acquisition of tumor tissue for predictive and pharmacodynamic studies.

4553 Background: AA, a potent oral CYP17A1 inhibitor is approved for treatment of mCRPC with a survival advantage of 4.9 months. In clinical practice, response evaluation remains challenging for pts with mCRPC. CTC conversion from CTC ≥ 5 to CTC < 5 with treatment predicts for improved overall survival in mCRPC. We hypothesized that pts continue to have durable disease stability beyond PSA progression on AA. Methods: Prostate Specific Antigen (PSA) responses, radiological responses and CTC conversion rates were retrospectively analysed in pts treated on AA at our institution. CTCs, PSA and imaging were obtained at predefined time points during these studies. Radiological and PSA progression were defined by standard Prostate Cancer Working Group Criteria II. Clinical progression consisted of worsening disease related pain, skeletal events or declining performance status.Pearson’s chi-squared test and the Kaplan-Meier method were used for this analysis. Results: 141 patients [ECOG Performance Status 0-2; Median Age: 69.7 (range 44.7-87.1); 85 post-docetaxel, 56 pre-docetaxel] received AA. The median duration of clinical and radiological stable disease (SD) was 16.8 months (n=55) and 5.6 months (n=75) in patients with a baseline CTCs count of ≤ 5 cells/7.5mls and ≥ 5 cells/7.5 mls respectively. In the 105 patients with documented PSA progression on AA there was a median 5.7-month delay in detecting radiological and/or clinical progression (95% CI: 4.2, 8.4; range 0.3, 35.6 months). Radiological and clinical SD of ≥ 1 year, ≥ 2 years and ≥ 3 years on AA was observed in 43/141 (30.5%), 21/141 (14.9%) and 12/141 (8.5%) respectively. Conclusions: Radiological and clinical disease stabilization beyond PSA progression is maintained in a high proportion of mCRPC patients treated with AA. Future studies should evaluate whether continued AA treatment beyond PSA and radiological progression can impact outcome.

e15134 Background: Sarcopenia, or skeletal muscle wasting, is an independent prognostic factor in advanced malignancy (Prado Lancet Onc 2008). Decreased muscle and increased fat are recognized side effects of androgen deprivation therapy. AA is a CYP17 inhibitor administered with corticosteroids (C), approved for treatment of advanced CRPC. AA reduces circulating androgens to ‘super-castrate’ levels; we hypothesized that AA + C would impact body composition. Methods: We retrospectively evaluated 54 CRPC pts treated on a Phase I/II trial. Pts received AA alone followed by combination AA + C on biochemical progression. CT scans at baseline, on AA alone and on AA + C were analyzed. Cross-sectional areas of fat and muscle were measured on 3 consecutive images at L4 using OsiriX 4.0. Muscle area was used to calculate skeletal muscle index (SMI); sarcopenia was defined as SMI 2/m2. Data were analyzed using t-tests and Kaplan-Meier analysis with overall survival (OS) measured from day 1 of AA. Results: Median duration on AA alone was 7.4 months (m; range 1.4-37.5); median duration on concurrent AA + C was 7.4m (range 0.9-46.2). Body composition did not change between two pre-treatment scans (n=29; median 3m apart). On AA alone there was a decrease in total fat (-8.5%, p=0.0001), visceral fat (-9.8%, p=0.0015) and muscle mass (-3.9%, p=0.0023) with a significant decrease in mean body mass index (BMI; -3.4 %, p=0.0118). Conversely AA + C was associated with increased total fat (+15.1%, p

e15136 Background: Median overall survival (mOS) in patients (pts) with metastatic prostate cancer progressing despite castrate levels of testosterone (mCRPC) was 13-16 months (m) in the pre-docetaxel era. These data, obtained from clinical trials, were used to construct currently available prognostic nomograms. We hypothesise that these models no longer reflect survival. Pts and physicians urgently require updated prognostic data on which to base management decisions. Methods: Pts with mCRPC treated on phase I-III trials at our institution were identified and data retrospectively collected. Predicted survival by Halabi and Smaletz nomograms were compared to calculated survival using Kaplan-Meier analysis. Cox model multivariate (MV) analysis used variables at referral, including performance status (PS), Gleason (GS), prostate specific antigen (PSA), lactate dehydrogenase (LDH), alkaline phosphatase (ALP), hemoglobin (Hb), visceral disease and albumin. Results: 423 pts with CRPC treated between 2003 and 2011 were included. At diagnosis median age was 62 years (y; 41.8 – 82.7); 226 (53.4%) had metastatic disease. Median interval from diagnosis to CRPC was 2.7y (0.2 – 21.7). At referral 248 pts (58.6%) were chemotherapy-naïve. Halabi and Smaletz models predicted mOS in chemo-naïve pts of 21m and 18m respectively, however the observed mOS was 32m (95%CI 28 – 38). Survival from CRPC was 43m (CI 37 – 46) and 39m (CI 34 - 44) in pre- and post-chemo pts, respectively. Conclusions: Despite aggressive disease characteristics, our pts lived significantly longer than predicted by current nomograms. MV analysis confirmed the importance of several previously identified prognostic factors. Survival data from this large cohort of CRPC pts should encourage men considering clinical trial participation. Previously developed nomograms no longer accurately predict survival.