Theranostics and hybrid imaging for somatostatin receptor-expressing tumors

Abstract

Conventional imaging tests like computed tomography (CT) cannot visualize somatostatin receptor (SSTR) expression on the tumor cell surface. For imaging of SSTR-expressing tumors conventional morphological imaging tests such as CT or magnetic resonance imaging (MRI) are employed. Molecular imaging of SSTR expression on the tumor cell surface, in particular by using (whole body) single photon emission computed tomography (SPECT) and positron emission tomography (PET), are considered the current standard of care. Only the use of CT enables for exact localization of putative sites of disease (hybrid imaging). Hybrid SPECT/CT and PET/CT are of utmost importance for staging and monitoring of treatment efficacy. SSTR-PET is superior to SPECT and the PET radiotracer 68Ga-DOTATATE has been approved in multiple countries. In addition, SSTR positivity revealed by SPECT or PET pave the way for apeptide receptor radionuclide therapy (PRRT). Such atheranostic approach enables for systemic or locoregional radiation with β‑emitting radionuclides, which are linked to the identical amino acid peptide used for PET or SPECT imaging. The prospective, randomized Netter‑1 trial has shown significant benefit for patients receiving PRRT. Acombined use of conventional and functional imaging tests is superior to conventional imaging alone and allows for identification of suitable candidates for atheranostic approach. In case of clinical suspicion or after having obtained histological evidence, hybrid SSTR-SPECT/CT or -PET/CT should be performed, preferably in adedicated molecular imaging center.