Early response assessment and bone flare phenomenon on 18F-fluorocholine positron emission tomography/computed tomography (FCH-PET/CT) in patients (pts) with metastatic castration-resistant prostate cancer (CRPC) treated with abiraterone acetate.

134 Background: In this prospective study, in patients with CRPC previously treated with docetaxel, we evaluated prostate specific antigen (PSA) and FCH-PET/CT for early response assessment to abiraterone acetate, and assessed frequency of early FCH-PET/CT discordant with PSA and clinical response. Methods: Twenty nine metastatic CRPC pts progressing after docetaxel chemotherapy received abiraterone acetate 1,000 mg daily with prednisone 5 mg twice daily in continuous 28-day cycles. Patients were evaluated monthly for serological PSA response and safety. FCH-PET/CT was repeated after 4-6 weeks and a CT scan was done after 3 months of abiraterone acetate. FCH-PET/CT bone flare was defined as the combination, after 3 months of therapy, of an interpreting radiologist’s report indicating progressive disease (PD) in context of a ≥50% decline in PSA, no PD at 3-month CT scan, with FCH-PET/CT improvement or stability 2-3 months later. Results: Three of 29 patients treated with abiraterone acetate did not perform...