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

Abstract

<b>BACKGROUND.</b> 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. <b>OBJECTIVE.</b> The purpose of this study was 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). <b>METHODS.</b> This prospective clinical trial enrolled 14 men with newly diagnosed high-risk prostate cancer and negative or equivocal conventional staging imaging for metastatic disease between January 2018 and February 2019. All patients underwent pretreatment ¹⁸F-fluciclovine PET/MRI including multiparametric prostate MRI; 12 underwent ¹⁸F-fluciclovine PET/MRI after surgery or between ADT and radiotherapy. Confidence in identification of the primary intraprostatic lesion and nodal metastases 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 SUV_mean, SUV_max, and volume of the MRI-defined intraprostatic lesion and SUV_max of suspicious lymph nodes on PET before and after initiation of ADT. Changes in SUV were analyzed using nonparametric Wilcox-on signed-rank tests. <b>RESULTS.</b> 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 three patients on MRI and seven patients on ¹⁸F-fluciclovine PET/MRI. After ADT, all patients showed decreased activity within the intraprostatic lesion and/or all suspicious lymph nodes. The primary lesion SUV_mean was 4.5 ± 1.1 (range, 2.7-6.5) before treatment and 2.4 ± 1.1 (range, 0.0-3.6) after initiation of ADT (<i>p</i> = .008). For suspicious lymph nodes, the pretreatment SUV_max was 5.5 ± 3.7 (range, 2.8-12.7) and the post-treatment SUV_max was 2.8 ± 1.4 (range, 1.4-5.5) (<i>p</i> = .03). <b>CONCLUSION.</b>¹⁸F-labeled fluciclovine PET/MRI shows potential utility in initial staging of high-risk prostate cancer and in evaluating response to ADT. <b>CLINICAL IMPACT.</b> Given the FDA approval and widespread availability of ¹⁸F-fluciclovine, the findings could have an impact in the immediate future in guiding initial management of patients with prostate cancer. <b>TRIAL REGISTRATION.</b> ClinicalTrials.gov NCT03264456.