Utility of 18F-Fluciclovine PET/MRI for Staging Newly Diagnosed High-Risk Prostate Cancer and Evaluating Response to Initial Androgen Deprivation Therapy: A Prospective Single-Arm Pilot Study.

Background: Despite advances in prostate cancer treatment, rates of biochemical recurrence remain high, relating to lack of detection of small-volume metastatic disease using conventional imaging for initial staging. Objective: To assess the potential use of 18F-fluciclovine PET/MRI for initial staging of high-risk prostate cancer and evaluating response to androgen deprivation therapy (ADT). Methods: This prospective clinical trial enrolled 14 men with newly diagnosed high-risk prostate cancer and negative or equivocal conventional staging imaging between January 2018 and February 2019. All patients underwent pretreatment 18F-fluciclovine PET/MRI including multiparametric prostate MRI; twelve underwent 18F-fluciclovine PET/MRI after surgery or between ADT and radiotherapy. Confidence in identification of the primary intraprostatic lesion and nodal metastates was independently rated on a 0-3 Likert scale by three readers with nuclear medicine experience for 18F-fluciclovine PET/MRI and three readers with abdominal imaging experience for MRI alone. Findings scored as 2 or 3 by at least two readers of a given modality were considered positive. A single reader measured SUVmean, SUVmax, and volume of the MRI-defined intraprostatic lesion, as well as SUVmax of suspicious lymph nodes, on PET before and after initiation of ADT. Changes in SUV were analyzed using non-parametric Wilcoxon signed-rank tests. Results: The biopsy-proven lesion in the prostate gland was accurately identified in all 14 patients on both MRI and 18F-fluciclovine PET/MRI. Suspected nodal metastases were detected in 3 patients on MRI and 7 patients on 18F-fluciclovine PET/MRI. Following ADT, all patients demonstrated decreased activity within the intraprostatic lesion and/or all suspicious lymph nodes. The primary lesion SUVmean was 4.5 ± 1.1 (range 2.7-6.5) before treatment and 2.4 ± 1.1 (range 0.0-3.6) following initiation of ADT (p=0.008). For suspicious lymph nodes, the pretreatment SUVmax was 5.5 ± 3.7 (range 2.8-12.7), and posttreatment SUVmax was 2.8 ± 1.4 (range 1.4-5.5) (p=0.03). Conclusion: Fluorine-18-labeled fluciclovine PET/MRI demonstrates potential utility in initial staging of high-risk prostate cancer and in evaluating response to ADT. Clinical Impact: Given the FDA approval and widespread availability of 18F-fluciclovine, the findings could have impact in the immediate future in guiding initial management of patients with prostate cancer. ClinicalTrials.gov registration number, NCT03264456.