New tracers beyond FDG in head and neck oncology.

Positron emission tomography with the glucose analogue 2-deoxy-2-[18F]fluoro-D-glucose (FDG-PET) is frequently used for staging and re-staging of squamous cell carcinomas of the head and neck region (HNSCC). HNSCCs generally demonstrate intense FDG uptake and FDG-PET has been found to be clinically useful in many situations. Nevertheless, several limitations of FDG-PET have also been identified. These include the physiologic uptake of FDG in several normal structures in the head and neck region as well as the unspecific FDG uptake by inflammatory processes. In order to overcome the limitations of FDG-PET tracers targeting amino acid transport, thymidine metabolism, hypoxia and antigen expression have been developed and tested in preclinical, as well as in initial clinical studies. While encouraging results have been obtained in small series of patients, none of the studied agents are likely to replace FDG-PET for staging and re-staging of HNSCCs, since their sensitivity for tumor detection appears limited. Nevertheless, they may provide complementary information on FDG-PET. Amino acid tracers may allow more specific detection HNSCC as compared to FDG-PET, and PET with [18F]fluorothymidine has shown encouraging results for monitoring changes in tumor proliferation during therapy. Using markers of hypoxia PET can potentially improve the efficacy of radiotherapy by increasing the radiation dose to hypoxic and thus more radioresistant tumors. Radiolabeled antibodies hold great potential for imaging drug targets and monitoring antibody therapy. Imaging of alpha(v)beta(3) integrins may allow characterization of tumor angiogenesis and monitoring of anti-angiogenic therapies. All these promising new applications of PET do, however, require more systematic clinical studies before they can be used for patient management.