Sarcopenia and altered body composition following abiraterone acetate (AA) and corticosteroid (C) treatment in men with castration-refractory prostate cancer (CRPC).

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 <52.4 cm 2 /m 2 . 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<0.0001) and visceral fat (+21.4%, p<0.0001) but no further change in muscle mass. Mean BMI significantly increased on the addition of C, returning to baseline levels (p< 0.0001). Overall, 13 pts (24%) were sarcopenic prior to commencing AA compared to 22 (41%) at the end of treatment. Pts who were sarcopenic at baseline had significantly reduced OS: 26.1m (95%CI 16.6 – 41) vs 46.5m (95%CI 28.6 – 57.5, p=0.0253). Conclusions: Treatment with AA alone resulted in decreased fat and muscle. AA + C increased body fat without further alteration in muscle mass. Changes in BMI did not reflect changes in body composition. Sarcopenia at baseline was a negative prognostic factor in this population.