Breast Cancer

Background

What is breast cancer?

Breast cancer is the most commonly diagnosed cancer in women, but accounts for less than 1% of cancer cases in men worldwide [1]. There is strong evidence linking female breast cancer to estrogen (e.g. hormone therapy, early menarche, late menopause, few pregnancies), obesity and physical inactivity, and alcohol consumption, but 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 insights regarding occupational risk factors could impact both women and men.

 

Known occupational risk factors
    • Exposure to x- and gamma-radiation [2]
Possible occupational risk factors
    • Night shift work [2]
    • Endocrine disrupting compounds (e.g. certain pesticides such as dieldrin, polychlorinated biphenyls (PCBs), plastic and rubber byproducts) [1,3,4]
    • Ethylene oxide [2]
    • Polycyclic aromatic hydrocarbons (PAHs) [3]
    • Organic solvents [5]
Key Findings

Increased risks of breast cancer were observed among both women and men for some occupational groups in the ODSS, which suggests a role for work-related risk factors in breast cancer etiology.

 

Nursing and other health workers

Elevated risks of breast cancer have previously been observed in workers involved in night or rotating shift work, including nurses [3]. Increased risk of breast cancer was observed among both male and female nurses in the ODSS. Health care workers such as radiological technicians may be exposed to x-ray and gamma radiation through medical imaging and radiation treatments [3]. Ethylene oxide, a suspected risk factor for breast cancer, is a chemical used in the sterilization of medical and dental equipment [6].

    • Nursing therapy and related assisting occupations: Women: 1.08 times the risk; Men: 4.73 times the risk
      • Nurses: Women: 1.19 times the risk; Men: 8.38 times the risk (note: this risk is based on a small number of cases)
      • Physiotherapists, occupational and other therapists: Women: 1.59 times the risk; Men: too few cases to report a result
    • Other occupations in medicine and health: Women: 1.18 times the risk; Men: 6.50 times the risk
    • Radiological technologists and technicians: Women: 1.63 times the risk; Men: too few cases to report a result
    • Hospitals: Women: 1.11 times the risk; Men: 2.15 times the risk
    • Diagnostic and therapeutic services industry, not elsewhere specified*: Women: 1.35 times the risk; Men: too few cases to report a result

*This industry includes laboratories (dental, medical, X-ray, etc.) providing analysis, diagnosis or treatment service to the medical or dental professions or to patients on prescription of a physician or dentist, and organizations such as the Victorian Order of Nurses, Red Cross Blood Transfusion Service, and St. John Ambulance.

Air transport

Risk of breast cancer among airline crew has been of interest because of exposure to cosmic radiation and circadian rhythm disruption [4]. Too few cases were observed among workers in the ODSS to examine this risk among specific occupation groups, or among men, but an increased breast cancer risk was observed among women for the overall industry.

    • Air transport industry: Women: 1.41 times the risk; Men: too few cases to report a result
White collar occupations

Individuals in these occupations generally have higher income and education, fewer children and work in sedentary jobs, which are characteristics that have been associated with breast cancer among women [7]. Elevated risks were observed among both men and women for many of these occupational groups.

    • Teaching and related occupations: Women: 1.27 times the risk; Men: 1.99 times the risk
    • Managerial, administrative, and related occupations: Women: 1.23 times the risk; Men: 1.53 times the risk
    • Clerical and related occupations: Women: 1.10 times the risk; Men: 1.45 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

 

Figure 2. Risk of breast cancer diagnosis among male workers employed in each industry group relative to all others, Occupational Disease Surveillance System (ODSS), 1983-2016

 

Figure 3. Risk of breast cancer diagnosis among female workers employed in each occupation group relative to all others, Occupational Disease Surveillance System (ODSS), 1983-2016 

 

Figure 4. Risk of breast cancer diagnosis among male workers employed in each occupation group relative to all others, Occupational Disease Surveillance System (ODSS), 1983-2016 

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 147 8,652 0.84 (0.72-0.99)
2/3 Forestry, Fishing and
Trapping		 7 479 0.76 (0.36-1.59)
4 Mines, Quarries and
Oil Wells		 9 477 0.82 (0.43-1.58)
5 Manufacturing 4,352 164,612 0.99 (0.96-1.02)
6 Construction 181 9,133 0.97 (0.84-1.13)
7 Transportation, Communication
and Other Utilities		 728 32,888 1.06 (0.98-1.14)
8 Trade 2,942 137,793 0.97 (0.93-1.01)
9 Finance, Insurance and
Real Estate		 195 8,721 0.82 (0.72-0.95)
10 Community, Business and
Personal Service		 8,212 348,864 1.03 (1.00-1.06)
11 Public Administration and
Defense		 1,685 68,996 1.07 (1.01-1.12)
         
* SIC: Standard Industrial Classification (1970)
† Hazard rate in each group relative to all others

 

Table 2. Surveillance of Male 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 <5 26,340 —
2/3 Forestry, Fishing and
Trapping		 6 10,218 1.65 (0.74-3.69)
4 Mines, Quarries and
Oil Wells		 7 22,731 0.73 (0.35-1.54)
5 Manufacturing 175 528,600 0.92 (0.76-1.11)
6 Construction 52 201,854 0.81 (0.60-1.08)
7 Transportation, Communication
and Other Utilities		 45 164,223 0.78 (0.57-1.05)
8 Trade 74 290,946 0.93 (0.73-1.20)
9 Finance, Insurance and
Real Estate		 5 15,233 0.82 (0.34-1.98)
10 Community, Business and
Personal Service		 102 249,212 1.54 (1.23-1.92)
11 Public Administration and
Defense		 57 121,577 1.26 (0.95-1.66)
         
* SIC: Standard Industrial Classification (1970)
† Hazard rate in each group relative to all others

 

Table 3. 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		 426 16,591 1.23 (1.11-1.35)
21 Natural sciences, engineering
and mathematics		 116 5,486 1.09 (0.91-1.31)
23 Social sciences and
related fields		 486 23,761 1.14 (1.04-1.24)
25 Religion <5 72 –
27 Teaching and related 1,117 38,139 1.27 (1.19-1.35)
31 Medicine and health 3,028 117,716 1.10 (1.05-1.14)
33 Artistic, literary,
recreational and related		 97 6,553 1.05 (0.86-1.29)
41 Clerical and related 2,636 100,514 1.10 (1.06-1.15)
51 Sales 1,480 75,966 0.96 (0.91-1.01)
61 Service 3,977 183,060 0.89 (0.86-0.92)
71 Farming, horticultural
and animal husbandry		 148 10,946 0.75 (0.64-0.89)
73 Fishing, hunting,
trapping and related		 <5 40 –
75 Forestry and logging <5 588 –
77 Mining and quarrying,
including oil and gas field		 <5 148 –
81 Processing
(mineral, metal, chemical)		 362 16,374 0.94 (0.84-1.04)
82 Processing
(food, wood, textile)		 733 31,854 0.95 (0.89-1.03)
83 Machining and related 545 21,324 1.01 (0.93-1.10)
85 Product fabricating,
assembling and repairing		 1,864 66,941 1.02 (0.97-1.07)
87 Construction trades 92 4,376 1.11 (0.90-1.36)
91 Transport equipment
operating		 306 14,142 1.05 (0.94-1.18)
93 Materials handling and related,
not elsewhere classified		 823 31,050 0.99 (0.93-1.06)
95 Other crafts and
equipment operating		 189 6,744 1.02 (0.89-1.18)
99 Other occupations not elsewhere classified 904 40,599 0.97 (0.91-1.04)
         
* CCDO: Canadian Classification Dictionary of Occupations (1971)
† Hazard rate in each group relative to all others

 

Table 4. Surveillance of Male 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		 9 14,275 1.53 (0.79-2.97)
21 Natural sciences, engineering
and mathematics		 7 20,834 0.98 (0.47-2.07)
23 Social sciences and
related fields		 5 6,845 2.65 (1.09-6.40)
25 Religion 0 52 —
27 Teaching and related 8 10,058 1.99 (0.99-4.01)
31 Medicine and health 24 17,079 4.83 (3.20-7.30)
33 Artistic, literary,
recreational and related		 0 8,406 —
41 Clerical and related 42 96,347 1.45 (1.05-1.99)
51 Sales 22 71,801 1.23 (0.80-1.89)
61 Service 73 187,246 1.25 (0.98-1.61)
71 Farming, horticultural
and animal husbandry		 8 39,184 0.77 (0.38-1.55)
73 Fishing, hunting,
trapping and related		 0 518 —
75 Forestry and logging <5 10,094 —
77 Mining and quarrying,
including oil and gas field		 5 12,895 0.97 (0.40-2.34)
81 Processing
(mineral, metal, chemical)		 18 62,825 0.89 (0.56-1.43)
82 Processing
(food, wood, textile)		 25 67,316 1.21 (0.81-1.80)
83 Machining and related 53 168,073 0.89 (0.67-1.19)
85 Product fabricating,
assembling and repairing		 71 261,229 0.74 (0.57-0.95)
87 Construction trades 65 211,243 0.88 (0.68-1.15)
91 Transport equipment
operating		 44 153,931 0.79 (0.58-1.08)
93 Materials handling and related,
not elsewhere classified		 33 121,910 0.92 (0.65-1.32)
95 Other crafts and
equipment operating		 12 21,542 1.49 (0.84-2.65)
99 Other occupations not elsewhere classified 51 174,561 0.98 (0.73-1.31)
         
* 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.

References

  1. Villeneuve S, Cyr D, Lynge E, Orsi L, Sabroe S, Merletti F, et al. Occupation and occupational exposure to endocrine disrupting chemicals in male breast cancer: a case-control study in Europe. Occup Environ Med. 2010;67(12):837–44.
  2. International Agency for Research on Cancer (IARC). List of Classifications by cancer sites with sufficient or limited evidence in humans, IARC Monographs Volumes 1-127 (2020).  
  3. Fenga C. Occupational exposure and risk of breast cancer (Review). Biomed Reports. 2016;4(3):282–92.
  4. Gray JM, Rasanayagam S, Engel C, Rizzo J. State of the evidence 2017: An update on the connection between breast cancer and the environment. Environ Health 2017;16(1):1–61.
  5. Labrèche F, Kim J, Song C, Pahwa M, Ge CB, Arrandale VH, et al. The current burden of cancer attributable to occupational exposures in Canada. Prev Med. 2019;122:128–39.
  6. US National Toxicology Program. Report on Carcinogens, Fourteenth Edition: Ethylene oxide. 2016.
  7. Johnsson A, Broberg P, Johnsson A, Tornberg ÅB, Olsson H. Occupational sedentariness and breast cancer risk. Acta Oncol. 2017;56(1):75–80.