Clinical Applications of Somatostatin Receptor (Agonist) PET Tracers beyond Neuroendocrine Tumors.

Rasmus Helgebostad,James Patrick Connelly,Abass Alavi,Mona-Elisabeth Revheim,Kristine Amlie,Kjersti Johnsrud

doi:10.3390/diagnostics12020528

Abstract

Somatostatin receptor (SSTR) agonist tracers used in nuclear medicine scans are classically used for neuroendocrine tumor diagnosis and staging. SSTR are however, expressed more widely in a variety of cells as seen in the distribution of physiological tracer uptake during whole body scans. This provides opportunities for using these tracers for applications other than NETs and meningiomas. In this qualitative systematic review, novel diagnostics in SSTR-PET imaging are reviewed. A total of 70 studies comprised of 543 patients were qualitatively reviewed. Sarcoidosis, atherosclerosis and phosphaturic mesenchymal tumors represent the most studied applications currently with promising results. Other applications remain in progress where there are many case reports but a relative dearth of cohort studies. [18F]FDG PET provides the main comparative method in many cases but represents a well-established general PET technique that may be difficult to replace, without prospective clinical studies.

Highlights

Somatostatin is a cyclic peptide hormone with two active forms consisting of either14 or 28 amino acids regulating specific and selective functions depending on the location
The peptide binds to the G-coupled receptor SSTR, one of a large class of cellular membrane receptor proteins with seven transmembrane segments containing a peptide binding region at the external surface and an internal signaling system based on G-proteins and changes in guanosine phosphorylation
The receptor acts as a switch that is activated by binding somatostatin

Summary

Introduction

Somatostatin is a cyclic peptide hormone with two active forms consisting of either14 or 28 amino acids regulating specific and selective functions depending on the location. Somatostatin-producing cells are typically neurons or endocrine-like cells found in high density in the central and peripheral nervous systems, the endocrine pancreas, liver, spleen and in the gut. They can be found in smaller numbers in the thyroid, adrenals, submandibular glands, kidneys, prostate, placenta blood vessels, and immune cells [1]. Somatostatin bears several endocrine functions including pituitary regulation of growth hormone (GH) and thyroid stimulating hormone (TSH, inhibiting GH/TSH secretion through somatostatin secretion from the hypothalamus).

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