Measurement of plasma chromogranin A remains the most commonly used biomarkers for both screening and monitoring of patients with gastro-entero-pancreatic neuroendocrine tumours (GEP-NET), despite several limitations that include: lack of a reference CgA standard; wide variations depending on the used assay in different laboratories; and varying sensitivity ranges from 60 to 90% with low specificity <50%, depending on the population studied.

Surprisingly, and to the best of our knowledge, only three studies with small numbers of participants have been published that have investigated possible effects of food intake on the measurement of CgA. Most have been performed in healthy controls or patients on treatment with proton pump inhibitors for chronic gastritis (up to n = 11 per group) but only one study has investigated patients with GEP-NET, where n = 6 patients with gastric NET were included.

In this study, the investigators aim to assess the time dependent effects of normally ingested diet (5-item English breakfast; or tea or coffee; or ongoing fasted state) on plasma chromogranin A measurements, using timed measurements over 180 min following an > 10 hours overnight fast, in a randomised double-crossover design. The investigators aimed to include 25 - 35 patients with a histologically confirmed diagnosis of a GEP-NET of varying primary tumour location, tumour stage, grade; and presence or absence of treatment with long acting somatostatin analogues; as well as 10 - 15 healthy controls. In an additional small subgroup of patients who are initiated on treatment with GLP-1 analogues i.e. for type 2 diabetes or obesity, the investigators aim to establish whether injection of GLP-1 analogues has any effects on plasma CgA measurements.

Inclusion Criteria:

GEP-NET patients:

• Confirmed diagnosis of NET
• Aged 18 or over
• Able to provide written informed consent
• Able to commit to 3 visits within a 4 week period
• Able to fast overnight
• Able to adequately read/write/speak English

CONTROLS:

• No known diagnosis of NET
• Aged 18 or over
• Able to provide written informed consent
• Able to commit to 3 visits within a 4 week period
• Able to fast overnight
• Able to adequately read/write/speak English

Exclusion Criteria:

- GEP-NET patients

• No confirmed diagnosis of a NET
• Under the age of 18
• Unable to provide written informed consent
• Pregnant women
• Any patients who are un well on the day of their routine appointment
• Unable to fast overnight
• Unable to adequately read/write/speak English

CONTROLS

• Confirmed diagnosis of NET
• Under the age of 18
• Unable to provide written informed consent
• Pregnant women
• Any patients who are un well on the day
• Unable to fast overnight
• Unable to adequately read/write/speak English