24 January 2011

What are NETs?

Neuroendocrine Tumours (NETs) are relatively uncommon, usually slow growing cancers. You may hear them referred to as GEP NETs, because they often arise in the cells of the stomach (gastro), intestines (entero) and the pancreas (pancreatic). There are a number of different types of NET. These are examples of the more common NETs:

• GI (gastrointestinal) NETs (used to be called ‘carcinoid’)
• Functioning and Non-Functioning Pancreatic Tumours
• Multiple Endocrine Neoplasias
• Gastrinomas
• Insulinomas
• Glucagonomas
• Phaeochromocytomas
• Vipomas
• Goblet Cell Carcinoids

Between 3-5 people per 100,000 are diagnosed with new cases of NETs each year in the UK. However because NETs can grow slowly and in some people produce such minor symptoms, doctors believe that there are probably thousands of people living their lives with NETs, but unaware.

It is quite common for NETs to be found incidentally during tests or treatments for other conditions, such as irritable bowel syndrome, crohns disease, peptic ulcer disease, gastritis or gallstones.

Most NETs occur as the primary site (the original site of the tumour) in the digestive system, but they can arise in other parts of the body such as the lungs and the pancreas.

How NETs are formed is still not fully understood. As with all forms of cancer NETs arise when cells multiply rapidly in the body. Normal cells in our body divide in a controlled manner but in cancer the control signals go wrong. This causes abnormal cells to form, which divide quickly resulting in tumour growth.

We do know that there are a number of different types of NETs but that they all arise from neuroendocrine cells and that they do all share certain similar biological features when you look under the microscope, we know they have a secretory function, that there is a small inherited risk with some of the tumour types and that a number of NETs have a syndrome associated with them.

NETs that start in the digestive tract are named according to the site where the tumour started. These are often named gastroenteropancreatic tumours or GEPs. Most gastroenteropancreatic tumours develop in the organs of the digestive system. They usually start in the cells of the stomach (gastro), intestines (entero) and the pancreas

For example:

Foregut tumours are tumours found in the lungs, the stomach, the pancreas, the gall bladder and the duodenum.

Midgut tumours are tumours found in the jejunum, ileum, appendix and right colon.

Hindgut tumours are tumours that are found in the left colon and rectum.

These NETs are more commonly known as carcinoids and they account for about 55% of all NETs diagnosed. Most NETs produce abnormally large amounts of hormones, which are chemicals made by the body to trigger its various functions. For example most carcinoid tumours produce excess serotonin and gastrinomas will produce and excess of gastrin.

Some NETs develop in the pancreas and within this group there are a number of names to describe the different types. The name that each type has is because of the hormone the tumour produces.

For example:

Insulinomas, gastrinomas, somatostatinomas and VIPomas.

There is also a group of tumours that are called non-functioning pancreatic NETs. These do secrete certain hormones and peptides like other NETs but the release of these chemicals do not cause an identifiable ‘syndrome’ or collection of symptoms. This can make diagnosis difficult and explains why so many cases are picked up incidentally.

There are a number of rarer NETs that are associated with a condition called Multiple Endocrine Neoplasia type 1 or MEN-1 for short. For information on this type of NET please contact AMEND. This is the association for multiple endocrine neoplasia disorders. Their website is www.amend.org.uk or you can call them directly on 01892 525308.

Lung carcinoid tumours are an uncommon type of tumour that starts in the lungs. They tend to grow slower than other types of lung cancers. They are made up of special kinds of cells called neuroendocrine cells.

To understand lung carcinoid tumours it helps to know something about the normal structure and function of the lungs, as well as the neuroendocrine system.

The lungs are 2 sponge-like organs in your chest cavity. Your right lung has 3 sections, called lobes. The left lung has 2 lobes. It is smaller because the heart takes up more room on that side of the body. The lungs bring air in and out, taking in oxygen and getting rid of carbon dioxide gas, a waste product of the body.

When you breathe in, air enters through your mouth and nose and goes into your lungs through the trachea (windpipe). The trachea divides into tubes called the bronchi (singular, bronchus), which divide into smaller branches called the bronchioles. At the end of the bronchioles are tiny air sacs known as alveoli.

A thin lining called the pleura surrounds the lungs. The pleura protects your lungs and helps them slide back and forth as they expand and contract during breathing. The chest cavity is called the pleural cavity.

Types of Lung Carcinoid:

Like most cells in your body, lung neuroendocrine cells sometimes go through certain changes that cause them to grow too much and form tumours.

There are 4 types of neuroendocrine lung tumours:

• small cell lung cancer
• large cell neuroendocrine carcinoma
• typical carcinoid tumour
• atypical carcinoid tumour
• Small cell lung cancer

Small cell lung cancer (SCLC) is one of the fastest growing and spreading of all cancers.

Large cell neuroendocrine carcinoma

Large cell neuroendocrine carcinoma (LCNEC) is a rare cancer that, except for the size of the cells forming the cancer, is very similar to SCLC in its prognosis (outlook) and in how patients are treated.

Typical and atypical carcinoid tumours

The other 2 types of lung neuroendocrine tumours are carcinoids.

Typical carcinoids grow slowly and only rarely spread beyond the lungs. About 9 out of 10 lung carcinoids are typical carcinoids.

Atypical carcinoids grow a little faster and are somewhat more likely to spread to other organs. Seen under a microscope, they have more cells in the process of dividing and look more like a fast-growing tumour. They are much less common than typical carcinoids.

Carcinoids are also sometimes also classified according to where they form within the lung.

Central carcinoids form in the walls of large airways (bronchi) near the centre of the lungs. Most lung carcinoid tumours are central carcinoids, and nearly all of these are also typical carcinoids.

Peripheral carcinoids develop in the narrower airways toward the edges of the lungs. Most peripheral carcinoids are also typical carcinoids.

Different NETs affect people in different ways in terms of how they grow, the symptoms they produce, whether or not they spread and how they spread. However all NETs share some similar characteristics. Gaining the histology (what the tumours look like under a microscope) is very important in order to classify the cancer into a type and therefore allow your team to be able to plan appropriate treatments. Although NETs share similar characteristics the differences in each type can make a difference to the diagnosis and the way your cancer may behave.

The most important aspect of the care of the NET patient is that the care is tailored to suit the individual and that this care is provided by a specialist in the field of neuroendocrine tumours.

Quality of life is paramount for the patient and so team work is essential to provide a solid plan of treatment and follow-up.

There has been much research work done by dedicated healthcare professionals and huge progress has been made in terms of understanding these tumours.

What we need to ensure is that patients get seen by these specialists in order to access all the knowledge available.

This picture gives an example of the different people you may see along your patient journey.