NETs are usually described by where in the body the abnormal cells come from. The most common locations where NETs develop are the digestive tract and the lungs.^1,3

NETs can also be described in the following ways:^1,3

• How fast the tumour is growing – ranging from low grade (slow growing) to high grade (fast growing)
• Whether extra hormones are being produced – functional tumours produce extra hormones that can cause certain symptoms in the body; non-functional tumours don’t produce extra hormones

Different types of NETs include:^1,3

• Gastrointestinal NETs – these can start in different areas of the large bowel or small bowel, and represent about 54% of all NETs
• Pancreatic NETs – start in the endocrine cells of the pancreas, and account for about 7% of all NETs; most are non-functional
• Lung NETs – develop in the lungs and represent about 25% of all NETs
• Merkel cell carcinoma – a fast-growing NET that involves the Merkel cells present in the top layer of the skin
• Neuroblastoma – usually starts in the adrenal glands (located on top of each kidney) and affects immature or developing nerve cells in children; more common in children under 5 years of age

Most NETs grow slowly over years, but some can grow quickly and spread to other parts of the body. During the early stages, NETs may not cause symptoms, or they may only cause general nonspecific symptoms that can commonly occur with other illnesses, such as tiredness or loss of appetite.^1,3

The types of symptoms caused by NETs will be different depending on the location of the NET and whether the NET is producing hormones.^1,3

The exact cause of most NETs is not known. Some risk factors for developing NETs may include:^1,3

• Genetic factors – NETs are associated with some rare inherited diseases 
• Pre-existing conditions – peptic ulcers may increase risk for NETs in the digestive tract; diabetes may increase risk for developing pancreatic NETs
• Age – most NETs affect people aged over 40 years
• Sex – NETs appear to be slightly more common in men than in women, and slightly higher again in black African men

Your doctor will discuss your specific symptoms with you. Different tests are used to diagnose NETs depending on those symptoms and where in the body the tumours are thought to be.^1,3

Tests used to assess for NETs include:^1,3

• Blood tests – usually include a full blood count to count the number of different types of blood cells and tests for different tumour markers
• Urine tests – measure levels of a chemical called serotonin that can be produced by NETs
• Endoscopy – uses a camera inserted down the throat into the stomach or into the anus and large bowel to view the gut; this test is performed under sedation to avoid discomfort
• Bronchoscopy – uses a thin tube with a light and lens inserted through the mouth or nose to view the lungs; this test is performed under sedation to avoid discomfort
• Computed tomography (CT scan) – takes three-dimensional pictures of several organs at the same time; used to help doctors plan surgery, if required
• Magnetic resonance imaging (MRI scan) – records detailed cross-sectional pictures (“slices”) of the inside of the body; used to show the extent of any tumours
• Positron emission tomography (PET scan) – produces three-dimensional colour images that show where any cancers are in the body
• Biopsy – removes a small sample of tissue from the affected area for closer examination; biopsies are performed using local or general anaesthetic
• Echocardiogram – uses an ultrasound to examine heart valves that can sometimes be affected by NETs

Surgery removes tumours and some surrounding healthy tissue

Uses a specific hormone to help slow tumour growth and the overproduction of hormones.

Chemotherapy uses medications to kill cancer cells or reduce their growth and spread

Radiation therapy uses radiation to destroy cancer cells in the affected area

Uses medications designed to target specific features of cancer cells to stop their growth and spread

Theranostics uses a PET scan to identify targets for selective drug delivery