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
    • Lindane
    • Pentachlorophenol
Possible occupational risk factors
    • 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.

    • 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.

    • 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
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.

    • 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.

    • 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.

    • 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
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.

    • 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.

    • 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
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.