GRPR and gastrin-producing neuroendocrine tumor: The overexpression of GRPR in various human malignancies (e.g. prostate cancer, breast cancer, GIST, gastrinomas, small cell lung cancer) with minimal expression in healthy tissues (except for the pancreas and the GIT), makes the GRPR a very appealing biomolecular target both for imaging and peptide receptor radionuclide therapy (PRRT).