Lymphoma a type of neoplasm that originates in lymphocytes (a type of white blood cell in the vertebrate immune system). They often originate in lymph nodes, presenting as an enlargement of the node (a tumor). Lymphomas are closely related to lymphoid leukemias, which also originate in lymphocytes but do not form tumors. There are many types of lymphomas, and in turn, lymphomas are a part of the broad group of diseases called hematological neoplasms.

Thomas Hodgkin published in 1832 the first description of lymphoma, specifically of the form named after him, Hodgkin's lymphoma. Since, many other forms of lymphoma have been described and many classifications proposed. The 1982 Working formulation classification became very popular. It introduced the category Non-Hodgkin lymphoma (NHL), itself divided into 16 different diseases. However, since these different lymphomas have little in common with each other, the NHL label is of limited usefulness for doctors or patients and is slowly being abandoned. The latest classification by the WHO (2001) lists 43 different forms of lymphoma divided in four broad groups.

Some forms of Lymphoma are indolent (e.g. Small lymphocytic lymphoma), compatible with a long life even without treatment, whereas other forms are aggressive (e.g. Burkitt's lymphoma), causing rapid deterioration and death. The prognosis therefore depends on the correct classification of the disease, established by a pathologist after examination of a biopsy. Chemotherapy is prescribed by an oncologist, radiation therapy by a radiation oncologist.

Although older classifications referred to histiocytic lymphomas, these are recognized in newer classifications as of B, T or NK cell lineage. True Histiocytic malignancies are rare and are classified as sarcomas.

Prevalence

According to the U.S. National Institutes of Health, lymphomas account for about five percent of all cases of cancer in the United States, and Hodgkin's lymphoma in particular accounts for less than one percent of all cases of cancer in the United States.

Because the whole system is part of the body's immune system, patients with a weakened immune system, such as from HIV infection or from certain drugs or medication, also have a higher incidence of lymphoma.

REAL classification

WHO classification

The WHO Classification, published in 2001 , is the latest classification of lymphoma and is based on the "Revised European-American Lymphoma classification" (REAL). This system attempts to group lymphomas by cell type, i.e., the normal cell type that most resembles the tumor. There are three large groups: the B cell, T cell, and natural killer cell tumors. Other less common groups, including Hodgkin's lymphoma, are also recognized. (ICD-O codes are provided where available.)