18F-Fluorocholine PET/CT for early response assessment in patients with metastatic castration-resistant prostate cancer treated with enzalutamide

Purpose: We investigated the role of 18F-methylcholine (FCH) PET/CT in the early evaluation of patients with metastatic castration-resistant prostate cancer (mCRPC) treated with enzalutamide. Methods: The study group comprised 36 patients with a median age of 72 years (range 48–90 years) who were treated with enzalutamide 160 mg once daily after at least one chemotherapeutic regimen with docetaxel. Patients were evaluated monthly for serological prostate-specific antigen (PSA) response. FCH PET/CT was performed at baseline and repeated after 3–6 weeks. Univariate and multivariate Cox regression models addressed potential predictors of progression-free survival (PFS) and overall survival (OS). Results: At a median follow-up of 24.2 months (range 1.8–27.3 months), 34 patients were evaluable for early FCH PET/CT evaluation of response, and of these 17 showed progressive disease (PD) and 17 had stable disease or a partial response. A decrease in PSA level of more than 50 % was observed in 21 patients. Early FCH PET/CT PD predicted radiological PD 3 months in advance of CT in 12 of 18 patients (66 %) and was discordant with the decrease in PSA level in 13 patients. In 6 of these, biochemical PD was confirmed in 2 months. In multivariate analysis, only decrease in PSA level and FCH PET/CT were significant predictors of PFS (p = 0.0005 and p = 0.029, respectively), whereas decrease in PSA level alone was predictive of OS (p = 0.007). Conclusion: This is one of the first studies to evaluate the role of FCH PET/CT as an early predictor of outcome in mCRPC patients treated with enzalutamide. Our preliminary results suggest that the combination of FCH PET/CT and decrease in PSA level could be a valid tool to predict PFS in mCRPC patients. PSA remains the single most important prognostic factor, while FCH PET/CT does not add more information on OS beyond that obtained from PSA. Further studies in larger populations are needed to confirm these data and to clarify the role of FCH PET/CT in predicting response to enzalutamide in mCRPC patients.