Effects of abiraterone acetate and enzalutamide on muscle and adipose mass in men with metastatic castration-resistant prostate cancer (mCRPC).

5088 Background: Abiraterone acetate (AA) and enzalutamide (MDV3100), two androgen receptor-directed compounds, have been shown to improve survival for patients with metastatic castration-resistant prostate cancer (mCRPC) progressing after Docetaxel.. Since these drugs might be used at an early-stage in the future, and skeletal muscle (SM) and adipose tissue (AT) are known to be prognosis parameters, the aim of this study was to evaluate the body composition changes in patients with mCRPC treated with AA and MDV3100. Methods: Patients included in AFFIRM (n=62 treated with MDV3100 and placebo n=28) and COU-AA-301 (n=24 treated with AA+Prednisone (P)10mg/day and placebo+P n= 13) trials at the Institute Gustave Roussy were included in the analysis. Cross-sectional areas (cm2) of visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT) and SM were assessed by computed tomography imaging at 3rd lumbar vertebra and were indexed for height (cm2/m2) with Slice-O-Matic software V4.3 at baseline, 3, 6 and 12 months of treatment. The data from patients treated with AA or MDV3100 were compared to placebo-patients and tissues changes were compared to baseline. We used the validated sarcopenic definitions as SM index less than 52.4 (cm2/m2). Results: For all cohort, median age was 69 years (range: 48-83), median weight was 79 kg (range: 47-150) and median BMI was 25.9 kg/m2(range: 18-46). At inclusion, 74 patients (58%) were overweight or obese (BMI>24.9 kg/m2), and only 2 patients were underweight (BMI<18.5kg/m2). 97 patients (81%) were sarcopenic, and 56 (75%) of overweight or obese patients were sarcopenic. Over 3 months, the patients from the entire cohort lost muscle mass (mean change: 4.5±7.5% (» 0.7 kg of muscle)) (P=0.01) . A non significant loss of SAT -4.6±19.2% and a non significant increase of VAT (+10.7±50.3% ) were observed. A similar pattern was observed at 6 months. There was no significant difference between body composition changes in treated groups and placebo. Conclusions: Sarcopenia is highly prevalent in patients with advanced CRPC. Unexpectedly, no difference in body composition changes was observed between patients treated with MDV3100 or AA and placebo.