Investigation of head and neck tumors with ⁶⁸Ga-FAPI, the new radiotracer

Introduction Positron-emission-tomography-computer tomography (PET-CT) with ¹⁸F-FDG as standard tracer is used for the preoperative staging of head and neck tumors, especially for the diagnosis of CUP (Cancer of Unknown Primary). However, in diagnosis of Waldeyer's pharyngeal rings using ¹⁸F-FDG it is not possible to distinguish between chronically inflamed and tumor tissues. The fibroblast activation protein (FAP) is overexpressed in tumor-associated fibroblasts (CAF), but not in healthy tissues, or in tissues with chronic inflammation. The aim of this study was to compare a new radiotracer, ⁶⁸Ga-FAPI that interacts selectively with FAP, with ¹⁸F-FDG for the diagnosis of head and neck cancer.

Material and Methods In this study, six patients with suspicion of tonsil cancer were included. ¹⁸F-FDG and ⁶⁸Ga-FAPI-PET/CT assays were performed pre-operatively. Afterwards, the Results from the histopathological examination of resected tumors and neck dissection specimens were compared with the Results of PET-CT images.

Conclusions Histopathological examinations confirmed that all patients had a tonsil cancer with regional lymph node metastasis. In PET-CTs, all tonsil cancers showed an intensive uptake of both tracers. In contrast to the uptake of ¹⁸F-FDG the healthy tonsil tissues didn`t shown any uptake of ⁶⁸Ga-FAPI tracer. Immuno-histochemical stains of tissue sections with an antibody raised against FAP confirmed the Results of ⁶⁸Ga-FAPI-PET-CT, i.e. only tumor tissues that incorporated ⁶⁸Ga-FAPI were stained positively by the antibody.

Summary The standard PET-tracer ¹⁸F-FDG is not tumor-specific. In contrast, the use of the ⁶⁸Ga-FAPI tracer Results in tumor-specific images. So it may allow for a precise detection of head and neck tumors with high specificity.

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Publication History

Article published online:
10 June 2020