Lymphoma is a general term for a group of cancers that originate in the lymphatic system. The lymphomas are divided into two major categories: Hodgkin’s lymphoma and all other lymphomas, called non-Hodgkin’s lymphomas. Hodgkin’s lymphoma was named after Thomas Hodgkin, an English physician who described several cases of the disease in 1832. Hodgkin’s lymphoma will represent about 12.7 percent of all lymphomas diagnosed in 2004.

Lymphomas are cancers that begin by the malignant transformation of a lymphocyte in the lymphatic system. The prefix “lymph-” indicates their origin in the malignant change of a lymphocyte and the suffix “-oma” is derived from the Greek word meaning “tumor”.

Lymphomas, including Hodgkin’s lymphoma, result from an acquired injury to the DNA of a lymphocyte. Scientists know that the damage to the DNA occurs after birth and, therefore, is acquired rather than inherited. The change or mutation of DNA in one lymphocyte produces a malignant transformation. This mutation results in the uncontrolled and excessive growth of the lymphocyte, and confers a survival advantage on the malignant lymphocyte and the cells that are formed from its multiplication. The accumulation of these dividing cells results in the tumor masses in lymph nodes and other sites.

Lymphomas generally start in lymph nodes or collections of lymphatic tissue in organs like the stomach or intestines. Lymphomas may involve the marrow and the blood in some cases. Spread from a lymphoma site is not unexpected. Lymphocytic leukemias originate and are most prominent in the marrow and spill over into the blood. They occasionally spread to involve the lymph nodes.

Causes and Risk Factors

The annual incidence of lymphoma has nearly doubled over the last 35 years. The reasons for this increase are not certain and are probably multiple. Immune suppression plays a role in some patients. Persons infected with the human immunodeficiency virus (HIV) have a much higher risk of developing lymphoma. The Epstein-Barr virus causes Burkitt lymphoma in Africa. The bacterium Helicobacter pylori is associated with the development of lymphoma in the stomach wall. These risk factors explain only a small proportion of the cases.
The principle cause of the increase in lymphoma is unknown. There is an apparent increase in lymphoma incidence in communities where farming is prevalent. Studies point to specific ingredients in herbicides and pesticides as being associated with lymphoma occurrence, but the quantitative contribution of such exposures to the frequency of lymphoma has not been defined.

The cause of Hodgkin’s lymphoma is uncertain. Many studies of environmental, especially occupational, linkages have been conducted with ambiguous results. For example, woodworking exposure has been associated with the disease, but causality has not been established. The Epstein-Barr virus has been associated with about one-third of cases of the disease. It has not been established conclusively as a cause of Hodgkin’s lymphoma, however. Persons infected with HTLV and HIV also have an increased probability of developing Hodgkin’s lymphoma.

Age-specific incidence rates of non-Hodgkin’s lymphoma are 3.0/100,000 at ages 20-24 for males and 1.7/100,000 for females. By ages 60-64, they are 52.2/100,000 for males and 36.1/100,000 for females.
The incidence of Hodgkin’s lymphoma among people under 20 years of age was 1.1 per 100,000 people in 2001.