Neuroendocrine tumors arise from the neuroendocrine system, a diffuse system in which the nervous system and the hormones of the endocrine glands interact. Most of the well-described adult neuroendocrine tumors are distinctive and arise from a known primary site, including the carcinoid, pheochromocytoma, and Merkel's cell tumors. A second group is poorly differentiated and may or may not have "neuroendocrine features" and acts aggressively.
Carcinoid Tumors
Carcinoid tumors can be benign or malignant; most arise from one of four sites: the appendix, small intestine, rectum, and bronchus. They also occur, although less often, in the stomach, pancreas, colon, liver, ovary, testis, and cervix. Symptoms can include a sudden flushing and reddening of the upper part of the body, especially the head and neck, a sudden increase in heart rate and blood pressure, and diarrhea. Depending on where the tumor arises, symptoms can also include abdominal pain, anemia, pneumonia, a cough, and spitting of blood. Carcinoid tumors can also occur without any symptoms at all. Various techniques, including a wide range of imaging modalities and blood tests for specific hormones or receptors, are used to discover the location and extent of the primary tumor. Treatment depends on the tumor's location and stage but includes surgery and possibly chemotherapy and radiation therapy.
Pheochromocytoma
Cancer of the adrenal medulla, the area located inside of the adrenal glands, is called pheochromocytoma. This condition often causes the adrenal glands to make too much of a group of hormones called catecholamines. Excessive amounts of these hormones may cause high blood pressure, rapid pulse, palpitations, anxiety attacks, fever, headaches, nausea, vomiting, and clammy skin. More than half of pheochromocytomas are not malignant. Pheochromocytoma, like cancer of the adrenal cortex, is diagnosed with blood and urine tests as well as imaging tests such as computed tomography (CT) scanning. Pheochromocytoma may arise as part of a condition called multiple endocrine neoplasia (MEN) syndrome, which can result in other cancers of the endocrine system and hormonal abnormalities. Treatment includes surgery, radiation therapy, or chemotherapy, alone or in combination, depending on whether the cancer has spread beyond the adrenal cortex.
Merkel's Cell Tumors
Merkel's cell tumors are cancers that form on or just beneath the skin, but sometimes are also thought to arise from underlying soft tissue. They are also known as neuroendocrine cancer of the skin. Merkel's cell tumors are predominantly found in Caucasian people between the ages of 60 and 80. Symptoms include lumps, most often on the face or scalp, which can appear in a range of colors from brown to red to blue. Merkel's cell tumors are fast-growing and often spread to other parts of the body. Surgery is the most effective treatment. To destroy any remaining cancer cells, doctors use radiation therapy. Physicians treat those whose cancer has spread with chemotherapy, but it is of limited value.
Neuroendocrine Carcinomas
These tumors are generally very undifferentiated and can be diagnosed only when a pathologist examines a tissue sample using specialized stains; these allow the pathologist to determine the subtype of the cells. Physicians may also test a patient's urine to determine if specific products related to this cancer, such as 5-HIAA, are elevated. Some neuroendocrine tumors have special structural characteristics that define them (for example, a Merkel's cell), but at least 60 percent are never distinguished beyond the diagnosis of "neuroendocrine carcinoma." The tumor can arise from a variety of locations, including the gastrointestinal tract, lung, and brain. Some tumor cells produce products that mimic hormones, while others do not produce anything to cause symptoms. Treatment includes surgery, radiation therapy, or chemotherapy, alone or in combination.
