Non-Hodgkin's Lymphoma - Introduction

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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 such as the digestive tract, central nervous system, and around the tonsils.

Cells Affected in NHL

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.

T-cell lymphomas, Hodgkin's disease, and certain leukemias and aggressive lymphomas are covered in the REAL classification but are not discussed in any depth in this report.

Groups by Slow or Fast Growth. Each non-Hodgkin's lymphoma is further defined by its grade, or how aggressive it is: