An analysis of sodium 18f-fluoride PET/CT and prostate specific antigen (PSA) changes in men with metastatic castration resistant prostate cancer (mCRPC).

Abstract

203 Background: Recently there has been growing evidence that 18F-Fluoride PET/CT has increased sensitivity relative to technetium-99m diphosphonate (Tc-99m MDP) bone scan for evaluating metastatic bone disease. This analysis studied changes in 18F-Fluoride PET/CT and evaluated associations with PSA changes for mCRPC patients (pts) on enzalutamide (enz). Methods: As part of a randomized phase II study evaluating enz with or without vaccine therapy, men with mCRPC electively underwent 18F-Fluoride PET/CT at 3 month (mos) intervals [NCT01867333]. At these points serum PSA was collected. Data was taken on max SUV and volume of presumed cancerous lesions and a variable, ΣSUV*Volume, was calculated which was defined as the sum of the products of SUV max and volume of cancerous lesions. Results: At the time of our analysis, 19 pts had PSA and PET/CT data for at least 2 time points within 1 year of initiating therapy. The median baseline PSA was 19.6 ng/ml (0.76-587). All pts had predominantly bone disease with 10 having small volume lymphadenopathy. Only 1/19 pts progressed by PSA Working Group criteria. An analysis found that 18/19 pts (95%) had an association between changes in PSA and ΣSUV*Volume. Of these 18 pts, 13 had a major ( > 50%) and 1 had a minor ( > 30%) PSA response and all 14 had an accompanying decrease in ΣSUV*Volume. For 11/14 pts with PSA responses, the change in ΣSUV*Volume paralleled the change in PSA at all time points, while for 3 pts an associated change between ΣSUV*Volume and PSA was delayed by 3 mos. 4/14 pts had short term responses lasting only 3 mos followed by PSA increases. For these 4 pts the changes in ΣSUV*Volume paralleled PSA changes, decreasing at 3 mos and increasing thereafter. Finally 4/18 patients had no PSA response to therapy. All 4 pts had increases in ΣSUV*Volume which paralleled rising PSA values. Conclusions: Preliminary data from a small cohort suggests that findings on 18F-Fluoride PET/CT are associated with PSA changes. This represents a substantial difference from standard Tc-99m MDP and further suggests that 18F-Fluoride PET/CT may provide a more sensitive analysis of bone disease. Additional data from this and other studies are required.