Abstract
1164
Objectives: ntroduction: Anti-1-amino-3-18F-fluorocyclobutane-1-carboxylic acid (18F-FACBC, Fluciclovine) is a synthetic non-metabolized leucine amino acid analog PET radiotracer. Leucine is actively transported into proliferating malignant cells in favor of other amino acids and is therefore of interest in molecular imaging of cancer processes. 18F-Fluciclovine uptake is primarily by sodium ion-independent amino acid transporters. These transporters, such as LAT1, work as an exchange system that brings in a preferential amino acid in exchange for a less essential one but do not increase the overall cellular levels of amino acids. LAT1 is overexpressed in several types of malignancy including prostate cancer and has been associated with angiogenesis, proliferation, and metastatic potential. Though amino acid imaging is believed to be less confounded by inflammatory uptake, upregulated amino acid transport also occurs in benign inflammation. Our aim is to present several cases of incidental extraprostatic benign and malignant findings in patients who had undergone 18F-Fluciclovine PET/CT and improve the interpretive skills of physicians. Methods: We reviewed a total of 140 cases of 18F-Fluciclovine PET/CT at our institute from 2016 and 2017 for cases of incidental extraprostatic uptake worrisome for malignancy with biopsy proven pathology or subsequent imaging which clarified the pathology. 5 cases of incidental extraprostatic findings were selected. Pertinent information such as PSA levels, additional imaging, and pathological reports was abstracted from the chart by the authors for confirmation of diagnosis. Results: - Case 1: F18-Fluciclovine PET/CT showed right parotid mass and cervical adenopathy with uptake. Pathology revealed poorly differentiated squamous cell carcinoma of the parotid with metastatic lymph nodes, as well as, metastatic melanoma to the cervical lymph nodes. - Case 2/A: F18-Fluciclovine PET/CT showed multiple pulmonary nodules with uptake. Decreased in size following androgen deprivation therapy. - Case 2/B: F18-Fluciclovine PET/CT showed cavitary lung lesion with uptake. Pathology resulted pulmonary adenosquamous carcinoma. - Case 3: Benign rib fracture with Fluciclovine uptake. - Case 4: Significant wall thickening of the rectum with intense localization of radiotracer. Pathology revealed metastatic poorly differentiated prostatic adenocarcinoma. Discussion: The FDA has approved the use of 18F-Fluciclovine in men with suspected prostate cancer recurrence based on elevated blood PSA levels following prior treatment. While 18F- Fluciclovine is used for localization of recurrent prostate cancer, physiologic uptake is seen within liver and pancreas as well as abnormal localization within inflammation and other types of cancer. Unexpected uptake beyond that ascribed to physiologic activity, especially if focal and intense whether accompanied by an anatomic abnormality on CT, should be further evaluated with clinical correlation, other imaging, or tissue sampling.