We investigated the role of 18F-Choline positron emission tomography/computed tomography (FCH-PET/CT) in the early evaluation and outcome prediction of abiraterone therapy in patients with metastatic castration-resistant prostate cancer (mCRPC). Abiraterone is an androgen synthesis inhibitor, which has proven highly effective in patients with mCRPC.
Forty-three pts with mCRPC 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 safety and serological PSA response. FCH-PET/CT was performed at the start of treatment and after 4-6 weeks of therapy in 42 pts. In 13 pts was also possible to repeat it after 3 months. A CT scan was performed at 3 months after abiraterone acetate therapy too. In addition to biochemical and CT evaluation, was defined “PET scan flare” a decline of PSA levels ≥ 50% associated to a worsening of FCH-PET/CT, without evidence of progression at CT. Univariate and multivariate Cox regression models addressed potential predictors of progression-free survival (PFS) and overall survival (OS).
One of the 43 patients treated with abiraterone acetate did not perform the follow-up FCH-PET/CT due to rapid PD and a consequent decline in performance status. The remaining 42 patients, median age 73 yrs (range 57-83 yrs), were suitable for evaluation. We divided pts into 2 groups on the basis of the modification in PSA serum levels: group A, with PSA decrease (n=25) and group B, increase in PSA serum level (n=17). FCH-PET/CT showed 3 complete response (CR) (7%), 11 partial response (PR) (26%), 6 stable disease (SD) (14%), and 22 progression disease (PD) (52%). CT outcome were: CR (n=1, 2%), PR (n=1, 2%), SD (n=28, 67%) and PD (n=12, 29%). FCH-PET/CT flare was observed in 6 of 42 (14%) evaluable patients.
In group A, FCH PET/CT highlighted a 17 non-progressing patients (CR, SD, PR) and 8 progressing pts (PD). In group B, 3 pts had SD at PET/CT, while 14 pt showed PD.
In univariate analysis, PSA decline and FCH-PET/CT response predicted PFS, while PSA decline and FCH-PET/CT (progression vs non progression) predicted OS. In multivariate analysis, only FCH-PET/CT (progression vs nonprogression) remained significant for PFS and OS (p = 0.022 and p = 0.027, respectively).
Early FCH-PET/CT can predict clinical outcome in CRPC beyond PSA response. These data support further larger studies on FCH-PET/CT for abiraterone monitoring and outcome prediction in patients with CRPC.