What are Neuroendocrine Tumors?
Neuroendocrine tumors (NETs) is the umbrella term for a group of unusual, often slow-growing cancers, which develop from cells in the diffuse endocrine system. They are found most commonly in the lung or gastrointestinal system, but they can also originate in other parts of the body such as the pancreas, ovary, and testes, among other sites.
What are Neuroendocrine Cells?
The diffuse endocrine system is made up of neuroendocrine cells found in the respiratory and digestive tracts. The respiratory tract includes the bronchial tubes and lungs. The digestive tract starts at the mouth and ends at the rectum.
Neuroendocrine cells are also located in endocrine glands, such as the adrenal glands, pancreas, thyroid and pituitary. These cells are also found in the ovaries and the testes.
NET cancers develop when these specialized cells undergo changes causing them to divide uncontrollably and grow into an abnormal tissue mass (tumor).
How are NET cancers formed?
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 the formation of abnormal cells, which divide quickly resulting in tumor growth. Most NETs occur without any hereditary link, but there are cases where NETs are present as part of a familial endocrine cancer syndrome such as MEN1, MEN 2, neurofibromatosis type 1 or Von Hippel Lindau.
Why are there different names for NET cancers?
This group of cancers was first identified as a specific disease in the mid 1800s, and the term carcinoid was given to them in 1907 to describe a tumor that grew much more slowly than normal cancers. However, by the 1950s, it became quite clear that these slow-growing tumors could be malignant and spread from one part of the body to another like other forms of cancer.
Nowadays, the description carcinoid tumor is being slowly replaced in medical literature by the term NETs or gastroenteropancreatic tumors (gastro – stomach, entero – intestines, and pancreatic – pancreas) or GEPs for short. However, some doctors do still use the term carcinoid tumor or just carcinoid when they refer to NETs that develop in the stomach, duodenum, small intestine, appendix, colon or rectum.
The terminology can be confusing. For example, a carcinoid may be described as a NET or a GEP-NET; an insulinoma may also be described as a pancreatic NET, a PNET, a PET or a NET.
What are the different types of NET cancer?
There are a number of different types of NETs and they all have a slightly different way of presenting themselves, both in terms of symptoms and how they look under a microscope.
Examples of NETs
Carcinoids – lung, thymic, gastric, duodenal, pancreatic, small intestine, appendiceal, colon, rectal, ovarian and carcinoid tumors of unknown origin (unknown primary)
Functioning and Non-Functioning Pancreatic Tumors:
- Multiple Endocrine Neoplasias
- Goblet Cell Carcinoids
The most common sites for NETs to occur are in the lung and digestive system, but they can also arise in other parts of the body such as the pancreas. The place where the NET first appears is called the primary site. However, the NET may spread and be found in other parts of the body e.g. the liver and lymph nodes, and if this occurs your doctor may refer to the NET as a secondary tumor or metastasis.
NETs are classified according to the area in which they are found:
Classification of NETs
Foregut tumors: found in the lungs, stomach, pancreas, gallbladder and duodenum
Midgut tumors: found in the jejunum, ileum, appendix and right colon
Hindgut tumors: found in the left colon and rectum
How do NET cancers affect the body?
NET cancers can have a number of different effects on the body. Some NETs produce abnormally large amounts of hormones and some have a related syndrome, such as carcinoid syndrome, which means that the hormones that are secreted cause noticeable symptoms like flushing, diarrhea, cramps, asthma-like wheezing, heart problems and skin changes.
The tumors that arise in the pancreas can be classified as functioning and non-functioning. The functioning tumors will produce a number of clinical syndromes that are related to where they originate. For example, an insulinoma will oversecrete insulin and gastrinomas are gastrin-secreting tumors. The non-functioning tumors, which account for around 30-40% of pancreatic tumors, secrete certain hormones and peptides like other NETs but the release of these chemicals does not cause an identifiable syndrome or collection of symptoms. This can make diagnosis difficult and explains why so many cases are picked up incidentally.
NET cancers may also spread (metastasize) to other parts of the body. The most common sites for these secondary cancers are the liver, bones and lymph nodes.
Why do NET cancers behave differently in different people?
Different NETs affect people in different ways in terms of how the tumor grows, the symptoms produced, whether or not they spread and how they spread. However, all NETs share some similar characteristics.
The histology (what the tumors look like under a microscope) is very important in order to classify the cancer into a type, and therefore allow the medical team to be able to plan appropriate treatment. Although NETs share similar characteristics, the diagnosis and the way the cancer may behave could be different.
The most important aspect of NET patient care is that it is tailored to suit the individual, and that this care is provided by a specialist in the field of NETs. Quality of life is paramount for the patient, and so teamwork is essential to provide a solid plan of treatment and follow-up.
There has been much research work done by specialist healthcare professionals and progress has been made in terms of understanding these tumors. It is important to ensure that people with NETs are seen by specialists in order to access all the knowledge available.
A NET cancer patient should ideally be referred to a center where there is a multidisciplinary team that works together to ensure the best outcomes for each patient. This team would normally include gastroenterologists, surgeons, oncologists, endocrinologists, radiologists, nuclear medicine specialists, histopathologists and clinical nurse specialists.
Can NET cancers be cured?
When caught at an early stage, NET cancers can often be cured with surgery. As with all cancers, if a surgical cure is possible, this should be the first line of treatment. Patients must still be followed for at least ten years to ensure there is no recurrence of the cancer. Unfortunately, many patients are diagnosed later on, when the cancer has spread to other parts of the body. Even when the tumors have spread, the disease and its symptoms can often be controlled for many years.