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What is a Tumor?
Cells are the building blocks of all life. All cells have highly specific functions, but not all cells have the same function. When cells that have similar functions are grouped together they form a tissue. Tissues when grouped together to perform a specific function are called organs. All cells of the human body have the same DNA (genetic language). Cell growth and replication is highly controlled and is encoded in each cell’s DNA. However if there are enough mutations (changes) within a cell’s DNA, a cell can grow and replicate uncontrollably.
A tumor is a mass formed by an abnormal growth of cells within the body. A tumor can be non-cancerous (benign) or cancerous (malignant). A tumor is considered cancerous when it has uncontrolled proliferation (abnormal growth) and can invade and destroy surrounding tissue. Malignant tumors can also have the ability to metastasize (spread to other organs of the body).
The neuroendocrine system consists of highly specialized neuroendocrine cells which act as an interface or junction between the nervous system and the endocrine system. The endocrine system is made up of cells whose function is to produce and secrete hormones into the bloodstream. Hormones are biochemical messengers that help to regulate many different processes within the body. The nervous system is composed of specialized cells (neurons) that control the activities of all body parts. A neuroendocrine cell is a cell which receives neuronal input (a signal from a nerve cell) and releases hormones in response to this signal.
A neuroendocrine tumor can develop anywhere there are neuroendocrine cells. The most common sites from which neuroendocrine tumors arise are the lungs, appendix, small intestine, rectum and pancreas (Yao, Hassan, Phan, Dagohoy, Leary, Mares, Abdalla, Fleming, Vauthey, Rashid, & Evans, 2008). Neuroendocrine tumors that arise in the pancreas are called pancreatic neuroendocrine tumors or islet cell tumors. When neuroendocrine tumors originate in other areas, they are often classified as carcinoid tumors.
Since neuroendocrine tumor cells are derived from neuroendocrine cells, many of these tumor cells can behave like cells they originated from and can secrete a variety of hormones. A functioning neuroendocrine tumor is one that secretes biologically active hormones causing a clinical syndrome. Non-functioning neuroendocrine tumors do not cause clinical syndromes.
Carcinoid tumors and pancreatic neuroendocrine tumors share similarities including often indolent behavior, ability to secrete biologically active hormones, and well-differentiated histology (Reidy, Tang & Saltz, 2009).
The majority of neuroendocrine tumors can be divided into two classes: carcinoid and pancreatic neuroendocrine tumors.
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