Objectives: L-[3-18F]-α–methyltyrosine (18F-FMT) is an amino-acid tracer for positron emission tomography (PET) and is used for tumor detection because malignant tumor cells accumulate 18F-FMT based on the increased expression of an amino-acid transporter. This study was conducted to investigate the usefulness of 18F-FMT PET in combination with fluorine-18-fluorodeoxyglucose (18F-FDG) PET for the diagnosis of sarcoidosis in patients with suspected malignancy.
Setting: Twenty-four sarcoidosis patients with suspected malignancy underwent 18F-FDG and 18F-FMT PET. The study included 17 patients with extrapulmonary manifestation mimicking malignant disease (13 patients with systemic lymphadenopathy, 3 of them with concomitant hepatosplenic processes; 3 patients with hepatosplenic processes without concomitant lymphadenopathy; and 1 patient with multiple bone lesions), 3 patients with occurrence of bilateral hilar lymphadenopathy in cancer patients, and 4 patients with multiple nodules mimicking pulmonary metastasis.
Results: All patients showed increased uptake of 18F-FDG and no increase in the accumulation of 18F-FMT in their lymphadenopathy. Standardized uptake values (SUVs) of 18F-FDG and 18F-FMT were 5.01 ± 2.15 and 0.77 ± 0.24, respectively (mean ± SD). All extranodal lesions such as liver, spleen, and bone were visually positive on 18F-FDG PET and negative on 18F-FMT PET. No neoplasm was confirmed in all patients. In a control group of patients with lung cancer, SUVs for 18F-FDG and 18F-FMT were 6.34 ± 2.52 and 1.54 ± 0.82, respectively.
Conclusion: The uptake of 18F-FDG was positive in the sarcoid lesions, and therefore 18F-FDG PET could not differentiate sarcoidosis from malignant disease. Use of 18F-FMT PET in combination with 18F-FDG PET may be the effective method to distinguish sarcoidosis from malignancy.