Risk Factors:

Non-Hodgkinâ ' s lymphoma is the fifth most common cancer in the United States. Each year, about 66,000 Americans were diagnosed with non-Hodgkin's lymphomas in 2007, and about 19,000 people die of the disease. Since the 1970s, NHL incidence rates have doubled. Part of the reason for this dramatic rise may be due to AIDS, which increases the risk for high-grade lymphomas.

The cause of non-Hodgkinâ ' s lymphoma is unknown, but certain factors may increase a personâ ' s risk of developing this cancer.

Age

Non-Hodgkinâ ' s lymphoma can develop in people of all ages, including children, it is most common in adults. The most common types of NHL usually appear in people in their 60s and 70s.

Gender

In general, NHL is more common in men than in women.

Race

Overall, the risk for NHL is slightly higher in Caucasians than in African-Americans and Asian Americans.

Family History

People who have close family relatives who have developed NHL may be at increased risk for this cancer. However, no definitive hereditary or genetic link has been established.

Infections

Viral or bacterial infections may play a role in some lymphomas. These include:

• Epstein-Barr virus (EBV), the cause of mononucleosis, is highly associated with Burkitt's disease and NHLs associated with immunodeficiency diseases. It is also a risk factor for Hodgkin's disease.
• The human immodeficiency virus (HIV), which causes AIDS, increases the risk for Burkitt lymphoma and diffuse large B-cell lymphoma
• The hepatitis C virus (HCV) may increase the risk for certain types of lymphomas.
• The Helicobacter pylori bacterium, which causes stomach ulcers, is associated withincreased risk for mucosa-associated lymphoid tissue lymphomas (MALT). (The use of antibiotics to get rid of the bacteria may cause remission in some patients who have an early stage form of lymphoma in an early stage.)

Immune System Deficiency Disorders

Patients with diseases or conditions that affect the immune system may be at higher risk for lymphomas:

• HIV-positive patients and those with full-blown AIDS are at higher risk for NHL, and the disease is more likely to be widespread in these patients than in those without the immune disease. Most AIDS-related NHLs are high-grade lymphomas.
• People who have organ transplants are at higher risk for NHL, probably due to multiple factors, including the drugs used to suppress the immune system and the transplanted organ itself.
• Patients who have had high-dose chemotherapy with stem-cell transplantation are at higher risk.
• Other immunodeficiency syndromes that put people at risk for NHL include Chediak-Higashi syndrome, ataxia-telangiectasia, B-cell lymphoproliferative syndrome, Bruton agammaglobulinemia, common variable immunodeficiency, and Wiskott-Aldrich syndrome.

Autoimmune Disorders

Patients with a history of autoimmune diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus, Hashimoto's thyroiditis, Crohn's disease, and Sjogren syndrome, are at an increased risk for certain NHLs, such as marginal zone lymphomas.

Chemical Exposure

Overexposure to a number of industrial and agricultural chemicals (such as pesticides, herbicides, and petrochemicals) has been frequently linked to an increased risk for lymphomas. The data, however, are not consistent.

Researchers are also investigating whether some chemotherapy drugs may increase the risk for later developing non-Hodgkinâ ' s lymphoma. At this point, it is not clear whether these drugs or the other cancers themselves increase risk. Other types of drugs, such as tumor necrosis factor (TNF) inhibitors that are used to treat autoimmune disorders, are also being studied as possible risk factors for lymphomas.

Radiation Exposure

People who have had radiation treatment for cancer, such as Hodgkinâ ' s disease, appear to have an increased risk for later developing non-Hodgkinâ ' s disease. The risk may be higher for patients treated with both chemotherapy and radiation.

Survivors of nuclear reactor disasters have an increased risk of developing NHL, as well as other types of cancers.

Lifestyle Factors

Lifestyle does not seem to be a major risk factor for NHL. Some studies have suggested that obesity may increase risk, but this association is not definite. Other studies have investigated the role of diet. Although some research has indicated an increased risk for diets high in consumption of red meat and lower risk for diets high in vegetables, for the most part a strong association remains speculative. There is no evidence that smoking increases the risk for NHL itself, although it has been linked with high-grade and follicular NHLs in people with lymphoma.