Adenoid Cystic Carcinoma show elevated tracer uptake in Fibroblast Activation Protein (FAP) specific PET/CT

Ziel/Aim Targeting Fibroblast Activation Protein (FAP) is a new diagnostic approach allowing the visualization of cancer associated fibroblasts. FAP is overexpressed in many cancers including head and neck cancers. Adenoid cystic carcinoma (ACC) is an aggressive and rare malignancy occurring most frequently in the salivary glands. Computed Tomography and Magnetic Resonance Imaging are standard imaging techniques for ACC. ¹⁸F-FDG PET/CT can also be used in ACC, but a significant portion of ACC does not show elevated FDG-uptake and imaging results may be obscured by the FDG-uptake of the salivary glands. In this study we retrospectively evaluated Fibroblast Activation Protein (FAP) specific PET/CT in 8 patients with recurrent ACC.

Methodik/Methods ⁶⁸Ga-labelled FAP-specific tracer molecules (FAPI-4 in 2 patients and FAPI-46 in 6 patients) were applied intravenously and PET/CT scans were taken 10, 60 and 180 minutes post injectionem. For all three time points, SUV_max and SUV_mean values of the ACC manifestations and background tissue were measured and Tumor-background Ratios (TBR) were calculated.

Ergebnisse/Results ACC showed elevated FAPI-uptake at all 3 time points. The average SUV_max was 8,91 +/- 2,26 after 10 minutes, 9,23 +/- 4,07 after 60 minutes and 7,98 +/- 2,47 after 180 minutes. The average SUV_mean was 5,00 +/- 1,54 after 10 minutes, 5,31 +/- 2,65 after 60 minutes and 4,29 +/- 1,13 after 180 minutes. Due to low background activity, we observed high TBRs of 3,35 +/- 1,52 after 10 minutes, 5,74 +/- 3,91 after 60 minutes and 4,51 +/- 1,76 after 180 minutes for SUV_max values and 3,92 +/- 1,53 after 10 minutes, 4,92 +/- 2,53 after 60 minutes and 3,95 +/- 0,82 after 180 minutes for SUV_mean values.

Schlussfolgerungen/Conclusions FAP-specific PET/CT imaging has shown promising preliminary results in 8 ACC patients. Due to low background activity especially in the head and neck region, FAP-specific PET/CT may be of future relevance for initial diagnosis, radiotherapy planning and follow-up of ACC. For the evaluation of its specific value in different clinical settings, further studies with larger cohorts are required.