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Locations of Non-Hodgkin's Lymphomas
Non-Hodgkin's lymphomas occur most often in lymph nodes in the chest, neck, abdomen, tonsils, and the skin. NHLs may also develop in sites other than lymph nodes. In Americans, this occurs most commonly in the digestive tract, although primary lymphomas of the central nervous system are on the rise. In Europeans, lymphomas outside the lymph nodes are more likely to develop around the tonsils.
Cells Affected in NHL
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About 85% of non-Hodgkin's lymphomas (NHLs) arise in B cells; the rest occur in T cells. Activation of a gene called BCL-2 is believed to be partly responsible for many B-cell lymphomas. This defect prevents apoptosis (a natural process whereby cells self-destruct) in the lymphoma cells.
Non-Hodgkin's Lymphomas Categories
There are more than 20 distinct types of non-Hodgkin's lymphomas. Most first arise in the lymph nodes, but about 20 - 30% of cases are now found outside the nodes, most often in the stomach, small intestine, skin, and brain.
Even experts disagree about the exact groupings. Lymphomas are categorized in a number of ways.
Classification by Cell Type, Appearance, and Genetic Make-up: The REAL System. Different classification systems for lymphoma have been proposed. The system used in this report is called REAL (Revised European-American Lymphoma Classification). It classifies all lymphomas by appearance, cell type, and genetic make-up:
- Non-Hodgkin's lymphomas are first grouped as B cell or T cell.
- Next, they are categorized by whether the B- and T-cell lymphomas were derived from immature (precursor) cells or mature (peripheral) cells.
- The peripheral B and T cells are then classified by their appearance, genetic make-up, and specific chemical "markers," which further identify them.
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