Single atypical metastases from Prostate Cancer as detected with Fluciclovine PET/CT: A Pictorial Essay

2042 Objectives: 1. To recognize and differentiate atypical single metastases from false positive Fluciclovine-avid and false negative non Fluciclovine-avid lesions.2. To understand the role of correlative imaging in the confirmation of atypical single metastatic lesion. 3. To provide examples of atypical single metastatic lesion from Prostate Cancer. 4. How to interpret these unexpected findings and direct further evaluation or recommendation if needed.Abstract: In the USA, it is projected in 2020 that Prostate Cancer (PCa) would be responsible for 191,930 new cases and 33,330 PCa-related deaths. After definitive therapy, 35% of PCa patients would develop biochemical recurrence (BCR) in the form of rising PSA and approximately 25% of these will progress to metastatic disease leading to significantly increased morbidity and mortality. Biochemical recurrence following radical prostatectomy is defined by the American Urological Association as a prostate-specific antigen (PSA) level greater than 0.2 ng/mL with a second confirmatory level. For patients undergoing external beam radiation, BCR is defined as a rise in PSA level of 2 ng/mL from nadir. In such patients, BCR is a critical juncture and may represent the last opportunity for curative therapy. When BCR is present, detection of recurrence as well as the location, distribution and number of metastatic sites would determine the choice of subsequent management. In the search of malignancy in patients with BCR, standard of care tests include Pelvic CT or MRI (to look for recurrence and/or pelvic nodal metastases) and a planar bone scan to look for skeletal metastases. However, standard of care testing has a low diagnostic yield of only 11% of patients for visualizing sites of disease. 18F-Fluciclovine is a synthetic amino acid PET tracer approved by the Food and Drug Administration in June 2016 for the detection of sites of recurrence in patients with BCR. In such patients, several studies have shown the higher diagnostic performance of 18F-Fluciclovine PET/CT compared to standard of care imaging modalities in the detection of metastases. Previous studies reported atypical metastases in the settings of a widespread disease. Recent clinical trials, however, are designed for oligometastatic disease, where potential for cure is highest. Such cure could be even higher is BCR cases with a single isolated metastasis. The role of Fluciclovine in the optimal identification of single metastatic disease is still lacking. This pictorial essay is to illustrate various representative cases of a single metastatic site from PCa that were detected with 18F-Fluciclovine PET/CT. All cases had pathologic confirmation and showed PSA response after therapy. Illustrative cases will include single skeletal lesions (lytic or sclerotic, with or without Fluciclovine avidity) in skull, sternum, and humerus, as well as an isolated adrenal metastasis. Also, careful interpretation of the CT scan as part of the PET/CT examination is of special importance in differentiating benign from malignant lesions. We will also show the appearance of some of these findings by other imaging modalities (diagnostic CT, MR, planar, SPECT and SPECT/CT) for further characterization.