NEN - the role of somatostatin receptor scintigraphy in clinical setting.

Detection of neuroendocrine neoplasms (NENs) and monitoring of their response to therapy is still challenging due to huge heterogeneity of that group of tumors. Actually, NENs visualization is mainly based on molecular imaging while in the past it was relied on less effective structural imaging including CT and MRI. Molecular imaging techniques in combination with structural imaging (hybrid imaging), especially in patients with well-differentiated NENs, in addition to morphological provide the functional information about tumor which benefits in a more accurate patient management, including more sensitive visualization of primary tumors, more precise staging and better therapy follow-up. Overexpression of somatostatin receptors (SSTR) on NENs' cell membrane was a basis for development of somatostatin receptor scintigraphy (SRS) using single photon emission tomography SPECT, which is today a well-established standard in molecular imaging of NENs, and further imaging improvement in the field of positron emission tomography (PET). Use of hybrid imaging (SPECT/CT, PET/CT) increased sensitivity of examination, mainly resulting in better detection of small lesions. Generally, somatostatin receptor imaging with PET/CT is an emerging technique, although still with limited access, but due to several advantages over SSTR SPECT/CT, should be used if available. It is worth mentioning, that both SSTR PET/CT and SSTR SPECT/CT have some limitations, such as relatively low detection rate of benign insulinomas, poorly differentiated GEP-NETs and liver metastases. For that reason further improvement of NETs imaging is necessary. The most promising new tracers' families are based on SSTR antagonists, 64Cu-radiolabeled ligands and glucagon-like peptide-1 receptor (GLP-1R) imaging. Finally, in case of poor-differentiated neuroendocrine cancers 18F-FDG PET/CT may be beneficial in comparison with molecular imaging based on somatostatin receptor modalities.