Peptide receptor therapies in neuroendocrine tumors

Neuroendocrine tumors (NETs) are relatively rare tumors, mainly originating from the digestive system, able to produce bioactive amines and hormones. NETs tend to be slow growing and are often diagnosed when metastatic. The localization of a NETs and the assessment of the extent of disease are crucial for management. Commonly used diagnostic techniques include morphological imaging (ultrasound, computerized tomography, magnetic resonance), and functional imaging (somatostatin receptor scintigraphy, positron emission tomography techniques). Treatment is multidisciplinary and should be individualized according to the tumor type, burden, and symptoms. Therapeutic tools include surgery, interventional radiology, and medical treatments such as somatostatin analogues, interferon, chemotherapy, new targeted drugs and peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogues. NETs usually over-express somatostatin receptors, thus enabling the therapeutic use of somatostatin analogues, one of the basic tools, able to reduce signs and symptoms of hormone hypersecretion, improve quality of life, and slow tumor growth. PRRT with somatostatin analogues 90Y-DOTATOC and 177Lu-DOTATATE has been explored in NETs for more than a decade. Present knowledge and clinical studies indicate that it is possible to deliver high-absorbed doses to tumors expressing sst2 receptors, with partial and complete objective responses in up to 30% of patients. Side effects, involving the kidney and the bone marrow, are mild if adequate renal protection is used. Moreover, a consistent survival benefit is reported. As NETs may also express cholecystokinin 2, bombesin, neuropeptide Y or vasoactive intestinal peptide receptors even simultaneously, the potential availability and biological stability of radio-analogues will improve the multireceptor targeting of NETs.