Neuroendocrine tumors develop from cells neuroendocrine stem cells. Previously, this tumor type was referred to as "carcinoid" meaning "cancer-like". This expression is now rarely used, and then primarily for neuroendocrine tumors in the small intestines or first part of the colon.
Hormone-producing cells are found in almost all of the body's organs, therefore these tumors can occur in most organs.
The prognosis depends on the degree of histological differentiation (see Grading). Patients with highly differentiated tumors and metastatic disease can live for years, whereas patients with non-resectable poorly differentiated disease will die within months, even with aggressive therapy.
The most common high differentiated neuroendocrine tumors originate from the small intestines (25%), lungs (20%), colon (8%), pancreas (7%), rectum (6%), stomach (5%), and veriform appendix (5%). Neuroendocrine tumors also occur in the thymus, adrenal glands, testicles, ovaries, breasts, thyroid gland, and in rare cases other organs (1).
The poorly differentiated tumors originates mainly from the lungs and the gastrointestinal tract.
The tumors are separated into:
- well differentiated neuroendocrine tumor
- poorly differentiated neuroendocrine carcinoma
A large number of patients with highly differentiated tumors live with the disease for many years without symptoms. There are, however, great differences in the degree of malignancy in tumors of the same organ, with the same grading, from patient to patient. While some tumors are benign with barely visible growth from year to year, others grow quickly and respond poorly to treatment.
In 2013 it was registered 1214 neuroendocrine tumors in Norway, 612 new cases were diagnosed in men and 602 in women.