A neuroendocrine tumour is a type of tumour made up of specialized cells called neuroendocrine cells. Neuroendocrine cells are part of both the nervous and endocrine systems of the body.
There are many different types of tumours made up of neuroendocrine cells. The name of the tumour depends on the location in the body and the way the tumour looks when examined under the microscope. Names given to tumours made up of neuroendocrine cells include carcinoid tumour, neuroendocrine tumour, and neuroendocrine carcinoma.
When examined under the microscope, most neuroendocrine tumours are made up of small to medium sized cells. The genetic material (chromatin) found inside the nucleus of the cell often looks like small dark dots on a white background. Pathologists call this “salt and pepper” chromatin pattern. The cells may stick together to form small structures called glands.
Pathologists sometimes perform a test called immunohistochemistry to confirm that the cells in the tumour are neuroendocrine cells. This test allows a pathologist to see proteins made by the cell. Most neuroendocrine cells make the proteins CD56, synaptophysin, and chromogranin. Tumour cells making these proteins are described as positive (reactive) while those that do not make these proteins are described as negative (non-reactive).
Because they are made up of neuroendocrine cells, some neuroendocrine tumours also make hormones. These neuroendocrine tumours are called functioning. Functioning neuroendocrine tumours can cause symptoms such as diarrhea, nausea, sweating, and head aches. Neuroendocrine tumours that do not produce hormones are called non-functioning. Non-functioning tumours may not cause any symptoms.
Neuroendocrine cells are found throughout the body. A neuroendocrine tumour can start in any location where neuroendocrine cells are normally found. Most neuroendocrine tumours start in the gastrointestinal tract (stomach, small bowel, and colon), rectum (the end of the colon just before the anal canal), appendix, pancreas, and lungs.
The behavior of a neuroendocrine tumour can range from non-cancerous to cancerous. Pathologists examine the tumour under a microscope and look for features that will help predict how the tumour will behave.
Microscopic features associated with cancerous tumours include:
The risk that the tumour will spread to another part of the body is higher if the pathologist sees dividing tumour cells or cell death. However, all neuroendocrine tumours have the potential to spread or to grow back after the tumour is removed. Tumour cells that travel to another part of the body are called a metastasis.
There are different types of neuroendocrine tumours and some are given a special name. The name of the tumour depends on where in the body the tumour starts and the kind of neuroendocrine cells that make up the tumour. Tumours that are more likely to behave in an aggressive manner are called a carcinoma.
Common types of neuroendocrine tumours include: