Evaluation of [18F]Fluoroethyl Triazole Labelled [Tyr3]-Octreotate Analogues for the Imaging of Neuroendocrine Tumours.

Neuroendocrine tumours (NET) are tumours derived from enterochromaffin cells, which are characterised by the expression of somatostatin receptors (SSTRs) on their surface. These tumours release substances into systemic circulation, resulting in episodic flushing, wheezing, diarrhoea, and eventual right-sided valvular heart disease. All of these symptoms negatively impact on patients' quality of life. The management of NET is primarily determined by the stage of disease. For patients with localised or limited disease the primary modality of therapy is surgery. Whilst patients with metastatic disease, undergo systemic therapy with palliative intent. Accurate imaging is therefore central to the management of this disease. Whilst computed tomography (CT) is useful in the localisation of NET, nuclear imaging using tumour-specific radiolabelled receptors are considerably more sensitive and specific methods for detecting NET and their metastases. The most commonly used positron emission tomography (PET) radiotracers used for the visualisation of NET are radiolabelled somatostatin analogs (SSAs) labelled with [68Ga]Ga-DOTA-peptides. The [68Ga]Ga-DOTA-peptide radiolabelled SSAs have significant limitations in terms of accessibility and low throughput. The team at Imperial College London developed a novel radiotracer, [18F]fluoroethyl triazole labelled [Tyr3]-Octreotate analogue ([18F]-FET-βAG-TOCA), in an attempt to overcome these limitations. The FETONET study was designed to have 3 parts. The FETONET study was designed to have 3 parts. Part A evaluated the biodistribution, dosimetry and safety of [18F]FET-βAG-TOCA. Uptake was assessed at multiple time points over a 4 hour period. The data was analysed and an optimal imaging time point determined. Part B of the FETONET study involved the performance of whole body static [18F]FET-βAG-TOCA PET-CT imaging, at the optimal time point previously established, within a larger cohort of patients. Part C comprised a prospective non-inferiority study that analysed the [18F]FET-βAG-TOCA PET/CT data collected within Part A & Part B and compared this to standard of care [Ga68]Ga-DOTA-peptide PET-CT imaging.

Inclusion criteria

• Written informed consent
• Age ≥ 18 years
• Histological diagnosis of NET of any site, except where ENETS criteria does not mandate histology for confirmation of diagnosis or patients who have a positive 68Gallium-peptide scan in whom NET diagnosis is pre-operatively definitive.
• Locally advanced or metastatic disease.
• Eastern Cooperative Oncology Group (ECOG) performance status of <2 (appendix A).
• Life expectancy > 3 months.
• Measurable disease defined as a lesion that can be accurately measured in at least one dimension with the longest diameter ≥10mm using conventional techniques.
• Somatostatin receptor imaging within 6 months. (if patient does not have somatostatin receptor imaging they may also be included provided they have measurable disease (≥10mm) on conventional imaging.
• Adequate organ system function as defined within Table 1.

Exclusion criteria

• Patients received chemotherapy within 3 weeks of study.
• Patients received radiotherapy within 4 weeks of study.
• Active uncontrolled infections, gastrointestinal disease, haemolysis or any serious co-existing medical illness.
• Psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule.
• Pregnant or lactating women.
• Females of childbearing potential who are unwilling to avoid pregnancy, for the duration of the study.
• Presence of any underlying medical conditions which in the investigators opinion would make the patients unsuitable for treatment.
• Patient not expected to be able to tolerate the scanning sessions.