Purpose: Standard imaging studies are limited as outcome measures for patients with metastatic prostate cancer. We tested the hypothesis that serial fluorodeoxyglucose positron emission tomography (FDG-PET) scans can serve as an outcome measure for patients with castrate metastatic prostate cancer treated with antimicrotubule chemotherapy.
Experimental design: FDG-PET scans were done at baseline, 4, and 12 weeks of treatment. The average maximum standardized uptake value (SUVmaxavg) was measured in up to five lesions and was tested as the quantitative outcome measure. Prostate-specific antigen (PSA) at 4 weeks and PSA, bone scan, and soft tissue imaging at 12 weeks were considered standard outcome measures. The change in SUVmaxavg that distinguished clinically assessed progression from nonprogression was sought.
Results: Twenty-two PET scans were reviewed and compared with PSA at 4 weeks; 18 PETs were compared at 12 weeks with standard outcome measures. Applying the PSA Working Group Consensus Criteria guideline that a 25% PSA increase constitutes progression to the SUVmaxavg, PET correctly identified the clinical status of 20 of 22 patients (91%) at 4 weeks and 17 of 18 patients at 12 weeks (94%). The accuracy of PET could be further optimized if a >33% increase in PSA and SUVmaxavg were used to define progression.
Conclusion: FDG-PET is promising as an outcome measure in prostate cancer. As a single modality, it can show treatment effects that are usually described by a combination of PSA, bone scintigraphy, and soft tissue imaging. Preliminarily, a >33% increase in SUVmaxavg or the appearance of a new lesion optimally dichotomizes patients as progressors or nonprogressors.