People whose immune systems are compromised -- as a result of inherited genetic diseases, HIV infection, or the immunosuppressive drugs administered to organ transplant patients -- have a higher risk of developing non-Hodgkin's lymphoma.
Certain viruses and bacteria may play a role in initiating the disease. Patients with the Epstein-Barr virus, the human T-cell leukemia/lymphoma virus (HTLV-1; most common in some parts of Japan and in the Caribbean islands), and Helicobacter pylori bacteria (which cause stomach ulcers) are at greater risk of some types of lymphoma.
Non-Hodgkin's lymphoma has also been linked to exposure to certain kinds of chemicals, including specific pesticides, solvents, and fertilizers. Herbicides and insecticides have been linked to non-Hodgkin's lymphoma in studies of farmers, pesticide applicators, and other occupational groups exposed to high levels of these chemicals. Contamination of drinking water with nitrate, a chemical found in fertilizers, may be associated with an increased risk of non-Hodgkin's lymphoma; this is a particular problem in agricultural areas, a National Cancer Institute study suggests.
