Breast Cancer

Background

What is breast cancer?

Breast cancer is one of the most commonly diagnosed cancers in women, but accounts for less than 1% of cancer cases in men worldwide. Although there is strong evidence linking many lifestyle and environmental risk factors to female breast cancer, such as exposure to estrogen (e.g. hormone therapy, early menarche, late menopause, few pregnancies), obesity and physical inactivity, and alcohol consumption, much less is known about potential occupational risk factors. Research on potential occupational risk factors for breast cancer has generally focused on exposure to some organic solvents and pesticides, polychlorinated biphenyls (PCBs), and shift work. Endocrine disrupting agents are suspected due to the role of hormones in breast cancer. Most evidence regarding breast cancer risk factors is based on female breast cancer due to the rarity of the disease among males. There have been few studies of occupational risk factors for male breast cancer and results have been somewhat inconsistent, but workplace exposures could impact both women and men.

 

Known occupational risk factors
    • Exposure to x- and gamma-radiation
Possible occupational risk factors
    • Shift work involving circadian rhythm disruption
    • Endocrine disrupting compounds (e.g. dieldrin insecticide, polychlorinated biphenyls (PCBs), plastic and rubber byproducts)
    • Ethylene oxide
    • Organic solvents
Key Findings

The greatest risks of female breast cancer were observed among management, administration and clerical, teaching, nursing, medical, and cleaning occupations.

White collar occupations

Individuals in these occupations generally have higher income and education and work in sedentary jobs, which are characteristics that have been associated with breast cancer. The elevated risk of breast cancer among both male and female teachers suggests the possibility of similar risk factors for the disease in this occupational group.

    • Management: Women: 1.6 times the risk; Men: 2.4 times the risk
    • Administrative and clerical: Women: 1.2 times the risk; Men: 1.6 times the risk
    • Teaching: Women: 1.5 times the risk; Men: 2.8 times the risk
Nursing and other medicine and health occupations

Elevated risks of breast cancer have previously been observed in workers involved in night or rotating shift work, such as nursing. Exposure to chronic low-dose ionizing radiation is also likely in other medicine and health occupations involving medical laboratory or radiation technology work. Ethylene oxide is a chemical used in the sterilization of medical equipment and is also a suspected risk factor for breast cancer.

    • Nursing therapy: Women: 1.2 times the risk; Men: 5.2 times the risk
    • Other medicine and health: Women: 1.3 times the risk; Men: 9.1 times the risk
Cleaning occupations

Cleaning occupations may involve a wide range of chemical exposures related to disinfection processes or dirt and dust removal. Exposure to agents such as volatile organic compounds (e.g. acetone, formaldehyde), acids, bases, and surfactants may be involved in these occupations, although these exposures have not been previously linked to breast cancer.

    • Janitorial/Cleaning: Women: 1.2 times the risk; Men: 1.7 times the risk
    • Other personal service: Women: 1.2 times the risk; Men: 4.4 times the risk
Relative Risk by Industry and Occupation

Figure 1. Risk of breast cancer diagnosis among female workers employed in each industry group relative to all others, Occupational Disease Surveillance System (ODSS), 1983-2016

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 breast cancer diagnosis among female workers employed in each occupation group relative to all others, Occupational Disease Surveillance System (ODSS), 1983-2016 

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 Female Breast Cancer: 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 149 8,654 0.72 (0.61, 0.84)
2/3 Forestry, Fishing and Trapping 7 479 0.67 (0.32, 1.41)
4 Mines, Quarries and Oil Wells 9 477 0.79 (0.41, 1.51)
5 Manufacturing 4,379 164,479 0.95 (0.91, 0.98)
6 Construction 181 9,133 0.92 (0.79, 1.06)
7 Transportation, Communication and Other Utilities 732 32,855 1.02 (0.95, 1.10)
8 Trade 2,968 137,716 0.92 (0.88, 0.96)
9 Finance, Insurance and Real Estate 196 8,712 0.97 (0.84, 1.12)
10 Community, Business and Personal Service 8,271 348,571 1.09 (1.06, 1.12)
11 Public Administration and Defense 1,696 68,920 1.12 (1.07, 1.18)
         
* SIC: Standard Industrial Classification (1970)    
† Hazard ratio in each group relative to all others    

 


Table 2. Surveillance of Female Breast Cancer: 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 430 16,568 1.54 (1.40, 1.70)
21 Natural sciences, engineering and mathematics 116 5,478 1.07 (0.89, 1.29)
23 Social sciences and related fields 487 23,723 1.04 (0.95, 1.13)
25 Religion <5 72  
27 Teaching and related 1,121 38,080 1.54 (1.44, 1.63)
31 Medicine and health 3,040 117,566 1.19 (1.14, 1.24)
33 Artistic, literary, recreational and related 97 6,549 0.80 (0.65, 0.97)
41 Clerical and related 2,651 100,407 1.16 (1.11, 1.21)
51 Sales 1,495 75,895 0.95 (0.90, 1.00)
61 Service 4,015 182,980 0.92 (0.89, 0.96)
71 Farming, horticultural and animal husbandry 149 10,944 0.59 (0.50, 0.69)
73 Fishing, hunting, trapping and related <5 40 —
75 Forestry and logging <5 589 —
77 Mining and quarrying, including oil and gas field <5 148 —
81 Processing (mineral, metal, chemical) 365 16,359 0.88 (0.79, 0.97)
82 Processing (food, wood, textile) 736 31,844 0.96 (0.89, 1.03)
83 Machining and related 546 21,312 0.96 (0.88, 1.05)
85 Product fabricating, assembling and repairing 1,875 66,851 1.01 (0.97, 1.06)
87 Construction trades 92 4,372 0.95 (0.78, 1.17)
91 Transport equipment operating 308 14,129 0.99 (0.89, 1.11)
93 Materials handling and related, not elsewhere classified 833 31,008 0.99 (0.92, 1.06)
95 Other crafts and equipment operating 194 6,734 1.03 (0.90, 1.19)
99 Other occupations not elsewhere classified 906 40,581 0.91 (0.86, 0.98)
         
* CCDO: Canadian Classification Dictionary of Occupations (1971)  
† Hazard ratio 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.