Table 8.2 Risk factors for non-Hodgkin’s lymphoma, by direction of association and strength of evidence
| Increases risk | Decreases risk |
Convincing or probable | Immune deficiency1,2,3 | |
| Some auto-immune disorders4 | |
| Various infections, including human immunodeficiency virus, type1 (HIV-1), Epstein-Barr Virus (EBV), human T-cell lymphotrophic virus type 1 (HTLV-1), hepatitis C (HCV), and Helicobacter pylori5 | |
| Occupational exposure to benzene, ethylene oxide, and formaldehyde6,7 | |
| Employment in the rubber manufacturing industry6 | |
| Family history of NHL, Hodgkin’s lymphoma or leukaemia8,9 | |
Possible | Occupational exposure to pesticides and trichloroethylene10,11 | Sun exposure16 |
| Tobacco smoking12 | Allergic conditions and/or atopy17,18 |
| Overweight/obesity13,14,15 | |
1 individuals with a weakened immune system; users of immunosuppressive drugs; 2 Grulich and Vajdic, 2005; 3 Grosse et al., 2009; 4 Ekstrom Smedby et al., 2008; 5 Bouvard et al., 2009; 6 Baan et al., 2009; 7 National Toxicology Program, 2008; 8 one or more first degree relative(s) affected; 9 Wang et al., 2007; 10 Mandel et al., 2006; 11 US Department of Health and Human Services, 2011; 12 Morton et al., 2005; 13 Larsson and Wolk, 2007; 14 Renehan et al., 2008; 15 Willett et al., 2008; 16 Kricker et al., 2008; 17 hay fever, asthma, food allergy, but not eczema; 18 Vajdic et al., 2009 |
Although lymphomas may occur in children, the following description of risk factors relates to NHL in adults.
The best described risk factor for NHL is immune deficiency (Table 8.2). Individuals who have had organ transplants, or who take immunosuppressive drugs to prevent organ rejection or to treat various autoimmune conditions (e.g. azathioprine and ciclosporin) have a high risk of NHL. Risk is also increased in individuals with some auto-immune disorders, including Sjorgen syndrome, systemic lupus and haemolytic anaemia. A variety of infection—including human immunodeficiency virus, type 1 (HIV-1) which causes AIDS, Epstein-Barr virus (EBV), which is a common member of the herpesvirus family, and hepatitis C virus (HCV)—can cause NHL, often acting via effects on immunosuppression or inflammation.
Occupational exposure to ethylene oxide (an organic compound used in the manufacture of products like polyethylene), benzene (an industrial solvent and precursor to basic industrial chemicals including drugs, plastics, synthetic rubber, and dyes) and formaldehyde (used in the production of industrial resins that are then used in the manufacture of products such as adhesives and binders for wood products, plastic and synthetic fibres) are all associated with NHL. Those exposed to pesticides through their work, or to tricholoroethylene, a hydrocarbon commonly used as an industrial solvent, may also have increased risk of NHL, but the evidence is less certain. Workers in the rubber manufacturing industry are also at increased risk, but due to the complexity of exposures in this industry, the causative agents have not yet been identified.
Risk of NHL is increased by around 50% in those who report first-degree relatives with NHL, Hodgkin’s lymphoma or leukaemia. In terms of lifestyle factors, current smoking may increase the risk of follicular lymphomas, but not other subtypes. A modest positive association between weight and NHL risk is evident in meta-analyses, but this may be limited to particular subtypes and/or to obese individuals. Increased recreational sun exposure may be associated with a modestly reduced risk of particular types of NHL, while individuals with allergic conditions, such as hay fever or asthma, or atopy may have slightly reduced risk of B-cell NHL.
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