Patients (pts) who develop biochemically recurrent prostate cancer (BRPC) after prostatectomy can be offered salvage radiation therapy (RT) to prostate bed and pelvis. The success of that strategy is contingent on the absence of metastases (mets). Standard imaging techniques including CT scan (CT) and bone scan (BS) have limited ability in localizing BRPC and better imaging is needed to guide therapy and prevent unnecessary salvage RT in pts with mets.
Pts were eligible if they developed BRPC defined as 2 PSA values of ≥0.2 at least 4 weeks after prostatectomy and had normal CT and BS. They underwent 18-F NaF PET/CT (NaF PET) and whole body diffusion weighted imaging MRI (DWI MRI) within 8 weeks of CT and BS. Biopsies of suspicious lesions were attempted. Positive finding on NaF PET required biopsy confirmation to constitute true positive (TP), DWI MRI interpreted as definitively positive was considered sufficient for TP status. Eight % detection rate of mets utilizing DWI MRI and/or NaF PET was considered worthwhile based on cost analysis of avoidance of unnecessary salvage RT.
Fifty six patients were enrolled between March 2014 and April 2016. Median age was 65 (49-86), median PSA was 0.46 (0.2-14.41). WBI MRI was suspicious for mets in 14 pts. Two pts with PSA of 9.25 and 1.55 had biopsy proven bone mets. Two pts with PSA of 4.44 and 2.27 had unequivocal bone mets on DWI MRI that were not biopsied. Two pts with PSA of 4.55 and 0.7 had enlarged pelvic lymph nodes that were not biopsied but considered metastatic by size criteria. Four pts with suspicious WBI MRI had negative biopsies. Four pts had lesions that could not be biopsied but remained stable on follow up imaging and were considered false positive. NaF PET scan was suspicious in 21 cases but no definitive mets were detected unless they were also visualized on DWI MRI. Three biopsies that were performed solely based on NaF PET results were negative.
DWI MRI detected site of recurrence in 6 pts (11%) with BRPC in whom standard CT and BS were negative. In 4 cases (7%) distant bone mets were noted precluding salvage RT from consideration. NaF PET did not contribute to the detection of metastatic disease beyond the MRI findings and was associated with high false positive rate.
Clinical trial identification
Legal entity responsible for the study
City of Hope Cancer Center
City of Hope Cancer Center
P. Twardowski: Consultant: Genentech, Medivation Speakers Bureau: Astellas, Medivation, Dendreon, Janssen, Bayer, Sanofi-Aventis Stock ownership: Exelixis.
S.K. Pal: consulting: Novartis, Astellas-Medivation, Pfizer, Aveo, Genentech. Exelixis, Glaxo, BMS.
C. Stein: Consulting, research funding: Roche Speakers Bureau: Sanofi-Aventis.
All other authors have declared no conflicts of interest.