Detection of Additional Primary Neoplasms on ¹⁸F-Fluciclovine PET/CT in Patients with Primary Prostate Cancer

The aim of this study was to evaluate the detection rate of incidental second primary neoplasms in patients with prostate cancer on 18F-fluciclovine PET/CT. Methods: Imaging reports and patient demographic data were retrospectively reviewed from 663 clinical 18F-fluciclovine PET/CT studies, performed in 601 patients for the assessment of their prostate cancer (643 - recurrence evaluation, 20 - initial staging) from August 2016 to April 2021. Maximum SUV (SUVmax) of the suspected second neoplasms was determined. The results of 18F-fluciclovine PET/CT were correlated with clinical and radiologic studies to determine the nature of the suspected second neoplasms. Results: Fiftyfive patients (9.1%) had findings suggestive of a second neoplasm. Thirty-nine of 55 had a known second neoplasm diagnosed before the PET/CT. An incidental second primary neoplasm was first suspected on 18F-fluciclovine PET/CT in 16 of 601 patients (2.7%). Three of the 16 patients had PET/CT suggestive of a meningioma that was corroborated on MRI. Of the remaining 13 patients, 11 had a tissue diagnosis confirming a malignancy. Second malignancies included renal cell carcinoma (RCC; 5/11; 45.5%), urothelial carcinoma (n = 2), multiple myeloma, chondrosarcoma, cutaneous squamous cell carcinoma, and squamous cell carcinoma of the esophagus and lung (n = 1, each; except for 1 patient with both esophageal and lung carcinomas). Among histopathologically confirmed malignancies, clear-cell RCC had the lowest uptake (SUVmax 3.4), and cutaneous squamous cell carcinoma had the highest uptake (SUVmax 13.6). Of the 2 patients with no histopathologic confirmation, 1 had ultrasound and MRI findings corroborating the diagnosis of RCC. The other patient had a solitary lung nodule suggestive of primary lung carcinoma and elected to undergo observation. Conclusion: Incidental findings consistent with a second primary neoplasm are not infrequently seen on 18F-fluciclovine PET/CT performed for assessment of prostate cancer (9.1%). Of the incidentally detected primary cancers, RCC was the most common (45.5%). These findings indicate the need for a careful analysis of 18F-fluciclovine PET/ CT images, due to the broad tumor imaging capabilities of this radiotracer.