Causes and risk factors of non-Hodgkin's lymphoma
The ultimate cause of non-Hodgkin's lymphoma is not known. There are some known risk factors but, even so, these risk factors do not account for more than a small proportion of the total number of cases of non-Hodgkin's lymphoma. In most patients with non-Hodgkin's lymphoma, no cause for the disease can be found. Moreover, most people who are exposed to one of the known risk factors do not develop non-Hodgkin's lymphoma.
So, it is important to remember that there is nothing that a person with non-Hodgkin's lymphoma has done to cause the disease.
Some of the most important risk factors are:
There is no evidence of any hereditary association with cases of non-Hodgkin's lymphoma. Therefore, the families of patients with the disease are no more likely to develop the disease than other people. Also, smoking is not linked to the development of non-Hodgkin's lymphoma.
Several viral infections have been shown to be associated with an increased risk of developing non-Hodgkin's lymphoma. These include:
People who are HIV-positive are more likely to develop non-Hodgkin's lymphoma than other people. The appearance of non-Hodgkin's lymphoma in an HIV-positive person may be an indication that full-blown AIDS is developing.
The increased risk probably arises because of the suppression of the immune system that HIV infection causes. AIDS-related non-Hodgkin's lymphoma often displays unusual features or occurs in unusual sites in comparison with other types of non-Hodgkin's lymphoma.
Epstein-Barr virus is a very common virus, affecting most people at some point in their lives, and either results in a short-lived infection or glandular fever. However, in an extremely small number of cases, it is linked to Burkitt's lymphoma and forms of non-Hodgkin's lymphoma associated with immunosuppression.
Human T cell leukaemia-lymphoma virus-1 (HTLV-1), originally from Japan and the Caribbean, is also an extremely rare cause of non-Hodgkin's lymphoma, with a long gap between infection with the virus and the development of the disease.
Bacterial infection is much less commonly associated with non-Hodgkin's lymphoma than viral infection. However, infection with Helicobacter pylori, which can cause stomach ulcers and affect the gullet, is associated with a relatively rare form of lymphoma known as a MALT lymphoma, which usually occurs in the stomach. Antibiotics to eradicate the bacterial infection often cure the condition, if given early enough.
Immunosuppressed people, whose defence systems are weakened, face an increased risk of developing non-Hodgkin's lymphoma. This is probably because control of B cell multiplication relies on the normal function of T cells. If T-cell function is abnormal, as is the case in immunosuppressed people, B cells can multiply in an uncontrolled way, increasing the chances of developing the disease.
One of the main causes of immunosuppression is the drugs that are given to prevent rejection of an organ transplant or bone marrow transplant. Patients who have had an organ transplant have an increased risk of developing non-Hodgkin's lymphoma.