Positron emission tomography/computer tomography in gastrointestinal malignancies: current potential and challenges

The use of 18F-Fluoro-D-deoxy-glucose -positron emission tomography/computed tomography (FDG-PET/CT) in gastrointestinal (GI)-malignancies may not be as straightforward as in many other cancers, but the potential is clearly there in select clinical settings. The challenges include the relative non-specificity of FDG, the variable degrees of physiologic FDG-uptake, and the heterogeneous FDG-uptake in different cell types within the GI-domain, which all together hamper the use in primary diagnostics. In general, the literature is older, heterogeneous, and based on stand-alone PET, which is now largely considered obsolete. There is emerging evidence for use of hybrid PET/CT, but the literature is still relatively sparse. The main indications are preoperative staging of distant metastases, not only in limited disease but also before curative treatment of limited metastatic disease. Controversies remain concerning liver metastases but improved technology boast well for the future role of FDG-PET/CT not least concerning equivocal findings on conventional imaging. In our opinion, an important upcoming indication is early response assessment, perhaps mostly in the neoadjuvant settings of upper GI-malignancies, but standardization of response assessment criteria is lacking before a more widespread implementation is feasible. Finally, there seems to be a significant role in recurrence detection, especially in CRC.