ON THIS PAGE: You will find some basic information about this disease and the parts of the body it may affect. This is the first page of Cancer.Net’s Guide to Neuroendocrine Tumor. To see other pages, use the menu. Think of that menu as a roadmap to this full guide.
About the endocrine system
The body’s endocrine system is made up of cells that produce hormones. Hormones are chemical substances that are carried through the bloodstream that have a specific effect on the activity of other organs or cells in the body.
About endocrine and neuroendocrine tumors
A tumor begins when healthy cells change and grow out of control, forming a mass. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body if it is not found early and treated. A benign tumor means the tumor can grow but will not spread. A benign tumor usually can be removed without it causing much harm.
An endocrine tumor  is a mass that begins in the parts of the body that produce and release hormones. Because an endocrine tumor develops from cells that produce hormones, the tumor can also produce hormones. This can cause serious illness.
A neuroendocrine tumor begins in the hormone-producing cells of the body’s neuroendocrine system, which is made up of cells that are a combination of hormone-producing endocrine cells and nerve cells. Neuroendocrine cells are found throughout the body in organs such as the lungs and gastrointestinal tract, including the stomach and intestines. Neuroendocrine cells perform specific functions, such as regulating air and blood flow through the lungs and controlling how quickly food moves through the gastrointestinal tract.
Types of neuroendocrine tumors
There are many types of neuroendocrine tumors. This section focuses on 3 specific types: pheochromocytoma, Merkel cell cancer, and neuroendocrine carcinoma. Other types of tumors that begin in hormone-producing cells are described in their own sections on Cancer.Net, including endocrine tumors , carcinoid tumors , thymoma , thyroid cancer , and islet cell tumors .
Pheochromocytoma. Pheochromocytoma is a rare tumor that begins in the chromaffin cells of the adrenal gland. These specialized cells release the hormone adrenaline during times of stress. Pheochromocytoma most often occurs in the adrenal medulla, the area inside the adrenal glands. This type of tumor increases the production of the hormones adrenaline and noradrenaline, which increase blood pressure and heart rate. Even though a pheochromocytoma is usually benign, it may still be life-threatening because the tumor may release large amounts of adrenaline into the bloodstream after injury. Among people with pheochromocytoma, 80% have a tumor in 1 adrenal gland, 10% have tumors in both glands, and 10% have a tumor outside the adrenal glands.
Merkel cell cancer. Merkel cell cancer is a highly aggressive, or fast-growing, rare cancer. It starts in hormone-producing cells just beneath the skin and in the hair follicles. It is usually found in the head and neck region. Merkel cell cancer may also be called neuroendocrine carcinoma of the skin or trabecular cancer.
Neuroendocrine carcinoma. Around 60% of neuroendocrine tumors cannot be described as anything other than “neuroendocrine carcinoma.” Neuroendocrine carcinoma can start in a number of places in the body, including the lungs, brain, and gastrointestinal tract.
The next section in this guide is Statistics . It helps explain how many people are diagnosed with this type of tumor and general survival rates. Or, use the menu to choose another section to continue reading this guide.