Molecular medicine imaging of neuroendocrine tumours

Neuroendocrine tumours (NETs) are a diverse, highly heterogeneous group of neoplasms derived from endocrine cells found in the neural crest. NETs typically display endocrine metabolism and slow growth, while displaying a wide range of presentations and clinical symptoms. Demonstrating typically small lesions, with varying anatomical localisation, diagnosis is typically in the advanced stages of tumour development. Molecular medicine provides a unique role in both the diagnosis and treatment of NETs. The diagnosis of NET is dependent upon clinical features, raised tumour biomarkers within the blood and urine, imaging of primary tumours and/or sites of metastasis and histopathologic results from tissue samples. Commonly used imaging modalities include conventional radiology (computed tomography (CT), magnetic resonance imaging (MRI) and transabdominal ultrasonography (US)), selective angiography, nuclear imaging techniques (eg somatostatin receptor imaging) and endoscopic US (EUS). Triple-phase CT and MRI are routinely used to provide anatomical localisation of primary tumour sites and initial staging of disease. Despite the heterogeneous nature of NETs, common characteristics exist among them. These tumours may possess special secretory granules, producing biogenic amines and polypeptide hormones, and express somatostatin receptors. Between 33-50% of NETs have active amine/ hormone production and may be classified as functional tumours. It is the shared characteristics of NETs that allows molecular imaging tracers to specifically target this wide range of neoplasms for imaging and treatment. This article aims to outline the most commonly used imaging methods for NET within molecular medicine.