18F-FBPA PET in Sarcoidosis: Comparison to Inflammation-Related Uptake on FDG PET.

A 68-year-old man with sarcoidosis showed high F-FDG uptake in the mediastinal and hilar lymph nodes on F-FDG PET, suggesting active inflammation. F-fluoro-boronophenylalanine (FBPA) PET showed no significant uptake in the mediastinal and hilar lymph nodes, suggesting its cancer specificity as a substrate of L-type amino acid transporter 1. F-fluoro-boronophenylalanine PET can be used for precise evaluation in oncology when the differentiation between inflammation and metastasis is inconclusive on F-FDG PET.

A 68-year-old man with tongue cancer and sarcoidosis underwent high-dose-rate interstitial brachytherapy to the primary cancer lesion (54 Gy/9 fr). Ten days later, 18F-FDG PET revealed high FDG uptakes in the mediastinal and hilar lymph nodes, suggesting active inflammation in a sarcoidosis granuloma (A–C, arrows; SUVmax, 8.05). In addition, 18F-FDG uptake was also seen in the pathway of the applicator implantation and radiation-induced inflammation, which was not observed in the pretreatment 18F-FDG PET (D and E, arrowheads). Uptake in the primary tumor region was not clear.

The following day after 18F-FDG PET, 18F-fluoro-boronophenylalanine (FBPA) PET was performed. No significant FBPA uptake was observed in the mediastinal and hilar lymph nodes (A–C, arrows), or in the inflammatory lesion from the right side of the tongue to the right submandibular region (D and E, arrowheads), suggesting its specificity as an l-type amino acid transporter 1 (LAT1).[1-4] LAT1 is a cancer-type amino acid transporter that shows minimal expression in inflammatory lesions.[1,5] 18F-α-methyl tyrosine, another LAT1-specific PET probe, was also reported to show no significant uptake in sarcoidosis lesions.[6-8] 18F-FBPA PET can be used for precise evaluation of oncology patients in which the differentiation between reactive uptake and metastatic uptake is inconclusive on 18F-FDG PET.