Molecular Imaging Radiotherapy: Theranostics for Personalized Patient Management of Neuroendocrine Tumors (NETs)

Neuroendocrine tumors (NETs) possess unique features including expression of peptide hormone receptors as well as the capacity to concentrate and take up precursor forms of amines and peptides making hormones that are stored in secretory granules within the tumor cells (APUD). The expression of somatostatin receptors on tumor cells have been widely explored during the last two decades starting with (111)In-DTPA-Octreotide as an imaging agent followed by (68)Ga-DOTATOC/TATE positron emission tomography scanning. The new generation of treatment includes (90)Yttrium-DOTATOC/DOTATATE as well as (177)Lutetium-DOTATOC/DOTATATE/DOTANOC treatment of various subtypes of NETs. The objective response rate by these types of PRRT is in the range of 30-45% objective responses with 5-10% grade 3/4 toxicity mainly hematologic and renal toxicity. The APUD mechanism is another unique feature of NETs which have generated an interest over the last two decades to develop specific tracers including (11)C-5HTP, (18)F-DOPA and (11)C-hydroxyefedrin. These radioactive tracers have been developed in centres with specific interest in NETs and are not available everywhere. (111)In-DTPA-Octreotide is still the working horse in diagnosis and staging of metastatic NETs, but will in the future be replaced by (68)Ga-DOTATOC/DOTATATE PET/CT scanning which provide higher sensitivity and specificity and is also more convenient for the patient because it is a one-stop-procedure. Both (90)Yttrium-DOTATOC/DOTATATE as well as (177)Lutetium-DOTATOC/DOTATATE are important new therapies for malignant metastatic NETs. However, the precise role in the treatment algorithm has to be determined in forthcoming randomized trials.