The incidence of non-Hodgkin lymphoma (NHL) rose during the latter half of the 20th century, and has now plateaued, although it is still rising in older people. It is currently the fifth most common cancer diagnosis in the United States. The reasons for the change in incidence are unknown.
NHL can occur at any age, but is more common among older people. The main symptoms are enlarged lymph nodes, fever, and weight loss. The cause is believed to be a combination of genetic and environmental factors. There are many subtypes of NHL, with different genetic factors. They can be aggressive (fast-growing) or indolent (slow-growing). A recent review article describes current medical knowledge of NHL risks.
Established risk factors are:
2. Male gender
3. Family history
4. Inherited immunodeficiencies, for B-cell lymphomas
5. Autoimmune conditions: Sjogren's syndrome for diffuse large B-cell lymphoma (DLBCL), celiac disease for T-cell lymphoma, systemic lupus erythematosus for B-cell lymphoma, and severe arthritis for all types
6. Infectious diseases: HTLV1, Helicobactor pylori, Epstein-Barr virus, HHV-8, hepatitis C, and HIV/AIDS
Unfortunately, the known risk factors account for only a small proportion of all NHL cases. The variety of types of NHL make it difficult to identify environmental factors that may have played a role. Hypothesized risk factors are:
2. Mild infections: mononucleosis, early birth order, and transfusions
3. Serum dioxin
5. Hair dyes
6. Occupational exposures to chemicals indicated by serum polychlorinated biphenyl level, occupational pesticides and solvent exposures
7. Dietary factors: nitrates, nitrosamines, meat, protein
Factors that appear to be protective are:
1. Allergies and asthma
4. Dietary factors: vegetables, fruits, fish, and green tea
Many individuals have the environmental risk factors but do not develop the disease. Research into the interaction between genes and environmental factors aims to reveal the biological mechanisms of lymphoma and to provide more options for effective prevention and treatment.