Impact of Enzalutamide Administration on Primary Prostate Cancer Volume: A Metabolic Evaluation by Choline Positron Emission Tomography in Castration-Resistant Prostate Cancer Patients

BackgroundEnzalutamide is active in advanced castration-resistant prostate cancer (CRPC) patients, in whom it has shown to be able to increase survival. We report the enzalutamide effect on primary prostate tumors, assessed by changes of metabolic tumor activity detected by 18F-fluorocholine-positron emission tomography/computerized tomography (18F-FCH PET/CT).Patients and MethodsWe treated 31 patients with pretreated metastatic CRPC in an enzalutamide named-patient program. All patients were initially evaluated and then followed up by means of repeated 18F-FCH PET/CT examinations. We identified most radiotracer-avid lesions, which were defined as specific regions of interest (ROIs): for each ROI we defined the maximum radiotracer standardized uptake value (SUVmax) and the threshold-based volume of interest (VOI) with a cutoff SUV value ≥ 2.5. In the 12 patients who did not receive a radical treatment for localized disease, the prostate was also considered an ROI.ResultsThe baseline prostate median SUVmax of 7.25 showed reductions of 25% (P = .012) and 43% (P = .009) after 3 and 7 months of enzalutamide treatment, respectively. The baseline median prostate VOI of 12.73 cm3 showed a reduction of 73% (P = .002) at 3 months and a reduction of 90% (P = .005) at 7 months.ConclusionIn addition to the metabolic changes of metastatic lesions observed with enzalutamide in CRPC patients, our data have shown significant volume reductions of the primary tumors according to 18F-FCH PET/CT evaluation. These results could suggest the potential of enzalutamide therapy for localized prostate cancer.