Definition of Lymphoma

Definition of Lymphoma
Lymphoma is a general term for cancers that develop in the lymphatic system.
Description of Lymphoma
Lymphomas account for 3 percent of all cases of cancer in this country.
The most common type of lymphoma is called Hodgkin's disease. All other lymphomas are grouped together and are called non-Hodgkin's lymphomas.
The lymphatic system is part of the body's immune defense system. Its job is to help fight diseases and infection.
The lymphatic system includes a network of thin tubes that branch, like blood vessels, into tissues throughout the body. Lymphatic vessels carry lymph, a colorless watery fluid that contains infection-fighting cells called lymphocytes. Along this network of vessels are groups of small, bean-shaped organs called lymph nodes. Clusters of lymph nodes are found in the underarms, groin, neck, chest, and abdomen.
Other parts of the lymphatic system are the spleen, thymus, tonsils, and bone marrow. Lymphatic tissue also is found in other parts of the body, including the stomach, intestines, and skin.
Like all types of cancer, lymphomas are diseases of the body's cells. Healthy cells grow, divide, and replace themselves in an orderly manner. This process keeps the body in good repair. In the non-Hodgkin's lymphomas, cells in the lymphatic system grow abnormally. They divide too rapidly and grow without any order. Too much tissue is formed, and tumors begin to grow. The cancer cells also can spread to other organs.
Malignant lymphocytes may be small and round or cleaved. Others may be large. Combinations of small and large cells may also be seen. Intermediate-sized lymphocytes with rapidly dividing cells are characteristic of aggressive (high-grade) lymphomas.
Within normal lymph nodes there are microscopic clusters (follicles) of specialized lymphocytes. In some malignant lymphomas, the lymphocytes arrange themselves in a similar pattern that is called follicular or nodular. Small cell and follicular lymphomas typically have a chronic course with an average survival of 6 to 12 years. In the more aggressive lymphomas, the normal appearance of the lymph node is lost by diffuse involvement of tumor cells, which are usually moderate-sized or large.
Hodgkin's disease, the most common lymphoma, has special characteristics that distinguish it from the others. Often it is identified by the presence of a unique cell, called the Reed-Sternberg cell, in lymphatic tissue that has been surgically removed for biopsy.
Hodgkin's disease tends to follow a more predictable pattern of spread, and its spread is generally more limited than that of the non-Hodgkin's lymphomas. By contrast, the non-Hodgkin's lymphomas are more likely to begin in extranodal sites (organs other than the lymph nodes, like the liver and bones).
There are about ten different types of Non-Hodgkin's lymphoma. Some types spread more quickly than others. The type is determined by how the cells look under a microscope (histology). The histologies are grouped together, based on how quickly they spread, into low-grade, intermediate-grade, or high-grade lymphomas.