Abstract

e15143 Background: C11- acetate (acetate) positron-emission tomogram (PET) has shown promise in detection of metastasis in prostate cancer in recent studies. Our study tested the feasibility of acetate-PET to predict early response to DP in CRPC. Methods: Men with metastatic CRPC for whom DP was indicated were enrolled in a prospective study of acetate-PET imaging and bone scans. Patients (pts) were imaged with both modalities at study entry and after 3 cycles of DP. DP was continued beyond cycle 3 until PCWG2-defined progression or toxicity. Treating physicians were blinded to acetate-PET results. No pts were on statins. The study was IRB-approved. Results: 6 pts with documented bone metastases were imaged (5 both pre and post-therapy.) Pre-therapy acetate-PET identified osseous metastases in all 6 pts. Remarkably, in one pt with previous radiation therapy, pre-therapy acetate-PET was negative for disease in the radiated area whereas bone scan showed persistent activity. The median number of DP cycles was 7 (5-16). 4 pts had ≥ 50% PSA decline. The median time to progression (TTP) was 5 months (mo). Of the 4 pts with PSA response, 2 had response on acetate-PET with TTP 5 mo and 10 mo respectively. One pt had > 50% PSA response but progression after 3 cycles based on PET, and met PCWG2 criteria for progression at 3.5 mo. The 4th pt with PSA response had stable findings on post-therapy PET and had 13 mo TTP. The pt who had no PSA response had stable post-therapy PET and had 2 mo TTP. Bone scan was stable in 3 pts, showed progression in 1pt and showed response in 1 pt. Conclusions: Response or progression on acetate-PET can be seen after a few chemotherapy cycles for CRPC. This study supports the exploratory inclusion of acetate-PET in future therapeutic clinical trials, with the potential to enhance the early prediction of treatment outcome. Acetate-PET might also allow more precise identification of viable target lesions than bone scan.

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