Neuroendocrine tumors (NETs) often present a diagnostic and therapeutic challenge. They are neoplasms that arise from cells of the endocrine (hormonal) and nervous systems. Many are benign, while some are cancers. It is a rare form of tumor with a global clinical incidence of 2.5 – 5 cases/100.000 per year. Although there are many kinds of NETs, they are often treated as a group because the cells of these neoplasms share common features, such as looking similar, having special secretory granules, and often producing biogenic amines and polypeptide hormones. NETs are believed to arise from various neuroendocrine cells present not only in endocrine glands throughout the body that produce hormones, but also diffusely in all body tissues.
An important category of NETs is the neuroendocrine tumors of the gastro-entero-pancreatic (GEP) system. These tumors originate from the diffuse endocrine system located in the gastrointestinal tract (carcinoids) and in the pancreas (insular tumors). The GEP NETs show extremely variable biological behavior and clinical course. The GEP tract has several different types of endocrine cells that produce more than 50 peptide hormones or amines. The GEP NETS can preserve and amplify the activity of the origin cells characterized by secretion of peptides, amines etc. These hormones lead to the manifestation of typical clinical symptoms by so called functional tumors. Some tumors may, however, be non-functional due to secretion of inactive hormones and/or dysfunctional hormone synthesis.
Many GEP NETs may be asymptomatic for years or can occur with obstructive symptoms. Due to this vagueness of symptoms the diagnosis is often delayed for several years. Symptoms from secreted hormones may prompt measurement of the corresponding hormones in the blood or their associated urinary products, for initial diagnosis. Given the diverse secretory activity of NETs there are many other potential markers, but a limited panel is usually sufficient for clinical purposes. Aside from the hormones of secretory tumors, Chromogranin A may be of great diagnostic value. This secretory protein, stored in dense-core granules of neuroendocrine cells, has been shown to be a very specific and sensitive marker for various forms of NETs. In recent years, improved diagnostic techniques and new therapeutic modalities have enhanced clinicians’ ability to detect and appropriately treat these rare and unique malignancies.
Endocrinology: The endocrine system is a complex collection of hormone-producing glands such as the pituitary, hypothalamus, pancreas, adrenal cortex, thyroid gland, parathyroid, and the gonads. There are in principle three forms of hormones, steroids, biogenic amines and peptides. Hormones act by binding to specific receptors in the target organand thereby control basic body functions such as metabolism, growth and sexual development. The amount of hormones produced by each gland is carefully balanced to generate needed effects. Too much or too little of a certain hormone can have effects throughout the body and cause various endocrine disorders. The endocrine glands secrete the hormones they produce directly into the bloodstream and are often controlled by trophic (stimulating) hormones. In addition to the classical endocrine glands, a number of tissues also secrete messenger substances/hormones involved in the cell to cell and tissue to tissue communication. Examples are the intestines, kidneys, liver, stomach and the heart.