Chest
Volume 131, Issue 4, April 2007, Pages 1019-1027
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Original Research
Chest Imaging
Diagnostic Usefulness of Fluorine–18-α–Methyltyrosine Positron Emission Tomography in Combination With 18F-Fluorodeoxyglucose in Sarcoidosis Patients

https://doi.org/10.1378/chest.06-2160Get rights and content

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.

Section snippets

Sarcoidosis:

Eligible patients were required to have histologically proven noncaseating epithelioid cell granuloma and at least one disease such that the possibility of coexistent malignancy could not be excluded, as follows: (1) extrapulmonary lesions mimicking malignant diseases including systemic lymphadenopathy, hepatosplenic involvement, or other lesions; (2) multiple nodular lesions mimicking pulmonary metastasis; and (3) the occurrence of BHL in a cancer patient. PET imaging using 18F-FDG and 18F-FMT

Control Group of Patients With Lung Cancer

Patient characteristics and results of PET findings are listed in Table 1. Of the 17 patients (13 men and 4 women; mean age, 61 years; range, 45 to 82 years), 9 patient had adenocarcinoma, 6 patients had squamous cell carcinoma, and 2 patients had NSCLC. PET imaging of 18F-FDG and 18F-FMT is shown in Figure 1.

Discussion

In the present study, 18F-FMT PET was useful for the evaluation of sarcoidosis in patients who were suspected of having malignant neoplasm. Since the uptake of 18F-FDG is nonspecific for malignant tumor, systemic disease of sarcoidosis is likely to mislead the diagnosis of metastatic disease. In all cases, coexistent malignancy could be clinically excluded in the study. The fact that one primary tumor and one metastatic lymph node were 18F-FDG positive but 18F-FMT negative highlights the

Conclusion

The present study found that the sarcoid lesions were positive on 18F-FDG PET and were negative on 18F-FMT PET in sarcoidosis patients. 18F-FMT PET may not replace 18F-FDG PET in the diagnosis of malignant lesions but may be a useful tool in combination with 18F-FDG PET in the diagnosis of sarcoidosis in patients with clinical suspicion of cancer or in characterizing individual lesions in patients with coexisting cancer and sarcoidosis. Further investigation is required to verify these results.

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    Our clinical trial registration number is ClinicalTrials.gov ID: NCT00369980.

    The authors have no conflicts of interest to disclose.

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