There are 3 types of stomach neuroendocrine tumours (NETs). The type of neuroendocrine tumour you have depends on a number of factors, including whether the stomach cells make the hormone gastrin.
The grade means how abnormal the cells look under the microscope. The grade gives doctors an idea of how quickly a cancer might grow and whether it will spread.
The tests and scans you have to diagnose a stomach NET give information about the type and grade. They also provide information about the stage of your NET. This means how big it is and whether it has spread. All this information together helps your doctor decide which treatment you need.
The most common type of stomach (gastric) neuroendocrine tumours is type 1. Between 70 and 80 out of 100 stomach NETs (between 70 - 80%) are type 1. They are slightly more common in women than in men.
They are often associated with a condition called chronic atrophic gastritis. This causes inflammation of the stomach cells, which leads to problems with stomach acid production.
It is rare that type 1 stomach NETs cause symptoms, so most people are diagnosed with it during tests for other problems.
These stomach NETs are usually benign and they are made up of cells that look similar to stomach cancer cell (grade 1). It’s rare that they spread to other parts of the body, or spread into surrounding tissues and cause damage.
Type 1 stomach neuroendocrine tumours are small (less than 1 to 2cm in any direction). And there is often more than one tumour, all of which are small, usually around 5mm. Often the normal stomach cells produce the hormone gastrin. So, the gastrin level in the blood is usually high.
Type 2 stomach neuroendocrine tumours are much less common than type 1. They are often small and there is usually more than one tumour. Although rare they are most common in people with the genetic hormonal condition MEN1. Or, in people with a tumour in the pancreas or duodenum called a gastrinoma. Your gastrin level might be high in the blood. And the stomach juices are very acidic.
It’s rare for type 2 tumours to cause symptoms.
Between 10 and 30 out of every 100 type 2 tumours (between 10 and 30%) spread to another part of the body.
Between 15 and 20 out of 100 neuroendocrine tumours (between 15 - 20%) are type 3. There is usually one, larger tumour (bigger than 2cm). They have often grown into nearby structures. Under a microscope, the cells look less like normal stomach cancer cells and they grow and divide quickly.
The level of gastrin in the blood is not usually high. They often produce no symptoms. Or you might have:
- weight loss
- low red blood cells due to iron deficiency (anaemia)
Type 3 tumours are most common in men over 50 years old. Over 50 out of 100 type 3 stomach NETs (over 50%) spread to another part of the body.
Grading is a way of dividing tumour cells into groups based on how the cells look under the microscope. This gives your doctor an idea of how quickly or slowly the tumour might grow and whether it’s likely to spread.
There are different ways to grade stomach NETs. In the UK, doctors use a system created by the World Health Organisation (WHO). The WHO grading system divides stomach NETs in 3 groups:
- grade 1 (neuroendocrine tumour G1 or WHO 1)
- grade 2 (neuroendocrine tumour G2 or WHO 2)
- grade 3 (neuroendocrine carcinoma G3 or WHO 3)
The grade of a stomach NET is based on how quickly the cells are dividing.
Ki–67 index test
The Ki-67 or mitotic index are ways of describing how many cells are dividing. A specialist doctor (pathologist) counts the number of NET cells that have started to divide into 2 new cells (mitoses) under a microscope. And a special stain measures the Ki-67 value.
Your doctor might tell you the number of cells that are dividing (number of mitoses), or you may see this on your pathology report. This helps your doctor decide which treatment you need.
Ki-67 index of 2% or lower
A Ki-67 index of 2% or lower means that fewer than 2 in every 100 cells (2%) are dividing. This is a grade 1 NET (NET G1).
Ki-67 index between 3% and 20%
This means that between 3 and 20 cells in every 100 cells (3% and 20%) are dividing. This is a grade 2 NET (NET G2).
Ki-67 index higher than 20%
A Ki-67 index of more than 20% means that more than 2 in every 10 cells (20%) are dividing. This is a grade 3 neuroendocrine carcinoma (NEC G3). They often grow and spread quickly.