Non-Hodgkin Lymphoma
Background
What is non-Hodgkin lymphoma?
Non-Hodgkin lymphoma (NHL) is a group of cancers of the white blood cells that perform immunological functions in the lymphatic system. NHL is the sixth most common cancer in Canada with an estimated 8,300 Canadians diagnosed in 2017. Men are more likely to be diagnosed than women.
There are few established risk factors for NHL and its etiology is not completely understood. However, exposure to the pesticide pentachlorophenol and the insecticide lindane are known risk factors. Exposure to ionizing radiation through medical imaging and infection with certain viral pathogens are non-occupational risk factors for NHL, though they may also be encountered in workplaces.
There are also a number of suspected occupational risk factors for NHL. There is some evidence that exposure to certain chlorinated organic solvents may increase risk, particularly trichloroethylene, which has been used in dry-cleaning and various industrial manufacturing processes. Other possible occupational risk factors for NHL include exposure to benzene, polychlorinated biphenyls, and certain pesticides.
Known occupational risk factors
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- Lindane
- Pentachlorophenol
Possible occupational risk factors
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- Benzene
- Trichloroethylene and dichloromethane (chlorinated solvents)
- Glyphosate, diazinon, malathion and DDT (pesticides)
- Polychlorinated biphenyls (PCBs)
Key Findings
Increased risks of NHL were found among groups in agriculture, mining, education, protective services, transportation, healthcare, and manufacturing. Because the causes of NHL are not well understood, the exposures that may drive these increases are not always clear.
Agriculture
Workers in farming occupations had an increased risk of NHL. This finding could be related to exposure to pesticides during work in agricultural settings. However, these results are based on a relatively small number of cases and should be treated with caution.
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- Farmers: 1.4 times the risk
Mining
Workers employed within the metal mining sector had an increased risk of NHL. However, it is not clear what is driving the increased risk.
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- Metal mines: 1.4 times the risk
- Gold quartz mines: 1.2 times the risk
- Uranium mines: 1.6 times the risk
- Miscellaneous metal mines: 1.4 times the risk
- Labourers in mining and quarrying: 2.1 times the risk
- Metal mines: 1.4 times the risk
Education
Workers in several occupations related to education services are at increased risk of NHL. The underlying risk factor for NHL within education workers is not clear, although it may be related to increased viral loading.
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- Secondary school teachers: 1.4 times the risk
- Elementary and kindergarten teachers: 1.2 times the risk
- Community college and vocational teachers: 2.7 times the risk
Protective service occupations
Workers in firefighting and police occupations are at an increased risk of NHL. It is not clear what risk factors are driving this risk, however, firefighters may be exposed to benzene in gasoline fumes, or to polychlorinated biphenyls (PCBs) and other chemicals during firefighting.
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- Firefighting occupations: 1.5 times the risk
- Policemen and detectives 1.2 times the risk
Transportation
Workers in transportation-related occupations had an increased risk of NHL. Those within these occupations are regularly exposed to engine exhaust fumes, which contain benzene.
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- Transport equipment operators: 1.2 times the risk
- Railway transport operators: 1.5 times the risk
- Motor transport operators: 1.2 times the risk
- Truck drivers: 1.2 times the risk
- Bus drivers: 1.2 times the risk
- Taxi drivers: 1.4 times the risk
- Railway conductors: 1.8 times the risk
- Other transport and related equipment operators (i.e. streetcar, snow removal): 2.2 times the risk
- Transport equipment operators: 1.2 times the risk
Health and medicine
Workers in nursing occupations had an increased risk of NHL. Similar to education services, employment in the health and medicine sector can expose workers to pathogens that could increase workers’ risk of infection.
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- Nurses: 1.2 times the risk
- Nursing aides and orderlies: 1.2 times the risk
- Nursing, therapy and related assisting occupations: 1.4 times the risk
Manufacturing
Workers in electrical equipment fabrication, assembly, installation, and repair occupations had an increased risk of NHL. These jobs involve potential exposure to chlorinated solvents and polychlorinated biphenyls (PCBs), which are suspected risk factors for NHL.
We expected to observe that workers employed in rubber and plastics manufacturing, printing, and chemical manufacturing would be at an increased risk of NHL, given what is known about occupational risk factors. However, workers within these industries were not at increased risk for this cancer. This may be related to declines in the use of chlorinated solvents and other industrial chemicals in Canada that are possible risk factors for NHL.
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- Electrical equipment fabricators, assemblers, and repairers: 1.1 times the risk
- Foremen: Electrical equipment assembly and repair: 1.7 times the risk
- Electrical equipment installers and repairers: 2 times the risk
- Electrical equipment fabricators, assemblers, and repairers: 1.1 times the risk
Relative Risk by Industry and Occupation
Figure 1. Risk of NHL diagnosis among workers employed in each industry group relative to all others, Occupational Disease Surveillance System (ODSS), 1999-2016

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater risk of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).
Figure 2. Risk of NHL diagnosis among workers employed in each occupation group relative to all others, Occupational Disease Surveillance System (ODSS), 1999-2016

The hazard ratio is an estimate of the average time to diagnosis among workers in each industry/occupation group divided by that in all others during the study period. Hazard ratios above 1.00 indicate a greater risk of disease in a given group compared to all others. Estimates are adjusted for birth year and sex. The width of the 95% Confidence Interval (CI) is based on the number of cases in each group (more cases narrows the interval).
Table of Results
Table 1. Surveillance of NHL: Number of cases, workers employed, and hazard ratios in each industry (SIC)
SIC Code * | Industry Group | Number of cases | Number of workers employed | Hazard Ratio (95% CI) † |
1 | Agriculture | 110 | 35,107 | 0.80 (0.67, 0.97) |
2/3 | Forestry, Fishing and Trapping |
57 | 10,719 | 0.92 (0.71, 1.20) |
4 | Mines, Quarries and Oil Wells |
193 | 23,221 | 1.27 (1.10, 1.46) |
5 | Manufacturing | 3440 | 694,717 | 0.89 (0.86, 0.93) |
6 | Construction | 936 | 211,510 | 0.95 (0.89, 1.02) |
7 | Transportation, Communication and Other Utilities |
1045 | 197,478 | 1.17 (1.09, 1.24) |
8 | Trade | 1686 | 429,819 | 1.03 (0.97, 1.08) |
9 | Finance, Insurance and Real Estate |
119 | 24,011 | 1.05 (0.88, 1.26) |
10 | Community, Business and Personal Service |
2382 | 600,174 | 1.14 (1.08, 1.20) |
11 | Public Administration and Defense |
961 | 191,034 | 1.07 (1.01, 1.15) |
* SIC: Standard Industrial Classification (1970) | ||||
† Hazard rate in each group relative to all others |
Table 2. Surveillance of NHL: Number of cases, workers employed, and hazard ratios in each occupation (CCDO) group
CCDO Code * | Occupation Group | Number of cases | Number of workers employed | Hazard Ratio (95% CI) † |
11 | Managerial, administrative and related |
143 | 31,006 | 1.50 (1.27, 1.77) |
21 | Natural sciences, engineering and mathematics |
120 | 26,352 | 1.19 (0.99, 1.42) |
23 | Social sciences and related fields |
105 | 30,711 | 1.35 (1.11, 1.64) |
25 | Religion | <5 | 129 | |
27 | Teaching and related | 223 | 48,489 | 1.44 (1.26, 1.64) |
31 | Medicine and health | 559 | 135,419 | 1.18 (1.08, 1.29) |
33 | Artistic, literary, recreational and related |
44 | 15,004 | 1.16 (0.86, 1.56) |
41 | Clerical and related | 881 | 197,493 | 1.15 (1.08, 1.24) |
51 | Sales | 474 | 148,200 | 1.09 (0.99, 1.20) |
61 | Service | 1638 | 371,204 | 1.14 (1.08, 1.20) |
71 | Farming, horticultural and animal husbandry |
175 | 50,254 | 0.93 (0.80, 1.08) |
73 | Fishing, hunting, trapping and related |
<5 | 556 | |
75 | Forestry and logging | 58 | 10,707 | 0.96 (0.74, 1.24) |
77 | Mining and quarrying, including oil and gas field |
104 | 13,038 | 1.25 (1.03, 1.51) |
81 | Processing (mineral, metal, chemical) |
356 | 79,355 | 0.98 (0.88, 1.09) |
82 | Processing (food, wood, textile) |
419 | 99,359 | 0.98 (0.89, 1.08) |
83 | Machining and related | 951 | 189,744 | 0.99 (0.92, 1.05) |
85 | Product fabricating, assembling and repairing |
1663 | 328,713 | 0.99 (0.94, 1.04) |
87 | Construction trades | 1058 | 216,043 | 0.98 (0.92, 1.05) |
91 | Transport equipment operating |
939 | 168,375 | 1.21 (1.13, 1.30) |
93 | Materials handling and related, not elsewhere classified |
696 | 153,279 | 1.01 (0.93, 1.09) |
95 | Other crafts and equipment operating |
158 | 28,358 | 1.07 (0.92, 1.25) |
99 | Other occupations not elsewhere classified | 969 | 215,565 | 1.04 (0.98, 1.12) |
* CCDO: Canadian Classification Dictionary of Occupations (1971) | ||||
† Hazard rate in each group relative to all others |
Please note that ODSS results shown here may differ from those previously published or presented. This may occur due to changes in case definitions, methodological approaches, and the ongoing nature of the surveillance cohort.