Neuroendocrine Tumors and Carcinoid Tumors

What are neuroendocrine tumors (NETs)?

Special cells in the body called neuroendocrine cells can act like both nerve cells and hormone-making cells. Neuroendocrine cells are scattered through organs in many parts of the body, such as the stomach, intestines, pancreas, and lungs.

As a group, tumors that start in these cells are often called neuroendocrine tumors (NETs). A newer, more accurate name for these tumors is neuroendocrine neoplasms (NENs).

NETs can grow at very different speeds. Some are slow-growing and may not cause problems for many years, while others can grow quickly. But even slow-growing NETs are usually considered cancers, because they have the potential to spread to other parts of the body.

What are well-differentiated neuroendocrine tumors (NETs)?

Well-differentiated neuroendocrine tumors (NETs) are a type of NET. Well-differentiated means the tumor cells still look and act somewhat like normal neuroendocrine cells. NETs usually grow more slowly than typical cancers, though some can grow faster.

Doctors grade these tumors as G1, G2, or G3, depending on how quickly the cells look like they’re dividing when seen under a microscope. Most are slower growing (G1 or G2). But even the faster-growing (G3) NETs still tend to behave differently from more dangerous cancers.

What are carcinoid tumors?

Carcinoid tumor (or just carcinoid) is an older term for certain well-differentiated NETs. These tumors usually grow more slowly and are most often found in the digestive system (such as the small intestine, appendix, or rectum) or lungs.

While doctors now usually use the term NET to describe them, “carcinoid” is still sometimes used, especially when referring to carcinoid syndrome, a group of symptoms caused by hormones released into the bloodstream. Symptoms of carcinoid syndrome include:

• Flushing of the skin (redness, warmth, often on the face or neck)
• Diarrhea (sometimes severe or watery)
• Wheezing or shortness of breath
• Rapid heartbeat (palpitations)
• Abdominal (belly) cramping or pain

What are neuroendocrine carcinomas (NECs)?

Neuroendocrine carcinomas (NECs) are poorly differentiated, meaning the cells look very abnormal under a microscope, and they tend to grow and spread quickly. Examples of neuroendocrine carcinomas include:

• Small cell lung cancer (SCLC)
• Large cell neuroendocrine carcinoma (LCNEC)
• Merkel cell carcinoma (MCC), an uncommon type of skin cancer
• Some fast-growing tumors of the pancreas or gastrointestinal tract

How are these tumors related?

• Neuroendocrine tumors (NETs) or neuroendocrine neoplasms (NENs) include all tumors that start in neuroendocrine cells. These range from slow-growing to fast-growing (aggressive) tumors.
• Well-differentiated neuroendocrine tumors (NETs) are made up of cells that still look somewhat like normal cells, and they tend to be slower growing.
• Carcinoid tumor is an older name for a subset of well-differentiated NETs. They are most often found in the digestive system or lungs. 
• Neuroendocrine carcinomas (NECs) are poorly differentiated, meaning the cells look very abnormal. These cancers tend to grow and spread quickly.

Information on specific neuroendocrine tumors

Find more detailed information on NETs, including symptoms, diagnosis, and treatment: