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 lymphoma and all other lymphomas, called non-Hodgkin lymphoma (NHL). The prefix "lymph-" indicates their origin in the malignant change of a lymphocyte and the suffix "-oma" is derived from the Greek suffix denoting "tumor." About 53 percent of the blood cancers that occur each year are lymphoma. Hodgkin lymphoma was named for Thomas Hodgkin, an English physician who described several cases of the disease in 1832. Hodgkin lymphoma will represent about 11.1 percent of all lymphomas diagnosed in 2008.
About 74,340 Americans will be diagnosed with lymphoma in 2008. This figure includes approximately 8,220 new cases of Hodgkin lymphoma (4,400 males and 3,820 females), and 66,120 new cases of NHL (35,450 males and 30,670 females).
Lymphoma results when a lymphocyte (a type of white blood cell) undergoes a malignant change and begins to multiply, eventually crowding out healthy cells and creating tumors that enlarge the lymph nodes or other parts of the immune system.
Lymphoma generally starts in lymph nodes or collections of lymphatic tissue in organs like the stomach or intestines. It may involve the marrow and the blood in some cases. Lymphoma may spread from one site to other parts of the body. Lymphocytic leukemias originate and are most prominent in the marrow and spill over into the blood. They occasionally spread to involve the lymph nodes.
Lymphoma Causes and Risk Factors
The annual incidence of NHL has nearly doubled over the last 55 years. The reasons for this increase are not certain and there are probably multiple causes. The increase began before the spread of the human immunodeficiency virus (HIV) within the population. Since the mid-1980s, the incidence of NHL in individuals infected with HIV has contributed modestly to the increase in lymphoma incidence. For those infected with HIV, the incidence of NHL is about 50 to 100 times the incidence rate expected in uninfected individuals.
Known risk factors explain only a small proportion of lymphoma cases. In specific geographic regions, infection with the Epstein-Barr virus is strongly associated with African Burkitt lymphoma in Africa. Epstein-Barr virus infection may play a role in the increased risk of NHL in persons with immune suppression as a result of organ transplantation and its therapy. The bacterium Helicobacter pylori causes stomach ulcers and is associated with the development of mucosa-associated lymphoid tissue (MALT) lymphoma.
Human T-cell lymphocytotropic virus (HTLV) is associated with a type of T-cell lymphoma in certain geographic regions in Southern Japan, the Caribbean, South America and Africa. About a dozen inherited syndromes can predispose individuals to later development of lymphoma. These inherited disorders are rare, but the concept of predisposition genes is under study to determine if they play a role in the sporadic occurrence of NHL in otherwise healthy individuals.
There is an apparent increase in NHL incidence in farming communities. Studies point to specific ingredients -- such as organochlorine, organophosphate and phenoxyacid compounds -- in herbicides and pesticides as being associated with lymphoma. However, the number of NHL cases caused by such exposures has not been defined.
Most cases of Hodgkin lymphoma occur in people who do not have any identifiable risk factors and most people with presumptive risk factors do not get the disease. The causes of Hodgkin lymphoma are uncertain. To illustrate: Many studies of environmental, especially occupational, linkages have been conducted with unclear results. Epstein-Barr virus has been associated with nearly half of cases. However, this virus has not been conclusively established as a cause of Hodgkin lymphoma. People infected with HTLV and HIV also have an increased probability of developing Hodgkin lymphoma. There are occasional cases of familial clustering, as with many cancers. There is an increased incidence of Hodgkin lymphoma in siblings of patients with the disease.
In the United States, NHL is the fifth most common cancer among males and females. The age-adjusted incidence of NHL rose by nearly 79 percent from 1975-2005.
Age-specific incidence rates of NHL are 2.9/100,000 at ages 20-24 for males and 1.9/100,000 for females. By ages 60-64, they are 53.9/100,000 for males and 39.2/100,000 for females.
The incidence of Hodgkin lymphoma among people under 20 years of age was 0.9 per 100,000 people in 2005.
For information on the treatment of Hodgkin lymphoma and NHL, read online or order the publication, Lymphoma: A Guide for Patients and Caregivers. For more detailed information see the booklets, Hodgkin Lymphoma and Non-Hodgkin Lymphoma .
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