The Canadian Cancer Society estimates that colorectal cancer will be the 3rd most commonly diagnosed cancer in Canada in 2020 [1] . Increased colorectal cancer screening is improving early diagnosis and treatment, but colorectal cancer remains the 2nd leading cause of cancer deaths [1,2]. Colorectal cancer risk is primarily attributed to lifestyle factors including obesity, physical inactivity, poor diet, alcohol consumption and smoking [3]. One study estimated that as many as 11-15% of cases may be attributable to occupational exposures [4]. However, there are no well established occupational risk factors for colorectal cancer.
Possible occupational risk factors
The greatest occupational risks for colorectal cancer in the ODSS appeared to be related to mineral and metal processing, and mining and quarrying. Excess risk was also observed for police officers, firefighters, truck drivers, and bus drivers. Occupational differences in lifestyle factors may play a significant role in the observed occupational differences in colorectal cancer risk. Sedentary work has been posited as a risk factor for colorectal cancer, but no excess risk was observed among most office workers in the ODSS. Non-occupational exposure to ionizing radiation is a risk factor for colorectal cancer. A 13% increased risk was observed among radiological technologists and technicians in the ODSS, but the number of workers employed in occupations and industries with radiation exposure is relatively small.
Workers in mineral and metal processing may be exposed to a variety of dusts, fumes and other substances, including asbestos, which may contribute to the excess colorectal cancer risk observed.
Miners may be exposed to ionizing radiation, which could contribute to risk of colorectal cancer. No excess was observed among uranium miners. Protective measures in uranium mines may more effectively protect miners than in other mine types [8]. Additionally, asbestos exposure may be a risk factor among some miners, however, too few cases were observed among asbestos miners in the ODSS to be able to examine this association among miners with the highest risk of exposure.
*mostly nickel miners
Workers in this group may be exposed to diesel engine exhaust, a possible risk factor for colorectal cancer.
Night shift work may be a colorectal cancer risk factor for firefighters and police officers. Firefighters may be exposed to asbestos in older buildings [9,10], which may contribute to the increased colorectal cancer risk observed for this group.
Occupational colorectal risk factors for transportation workers may include sedentary work, night shift work, and exposure to diesel engine exhaust.
Excess risks were observed among several additional occupational groups in the ODSS. The excess risk among service station attendants may be linked to diesel engine exhaust exposure, but occupational colorectal cancer risks among most of these groups is unclear. Occupational differences in smoking may be a factor. Exposure to ionizing radiation is the only known occupational risk factor for colorectal cancer, and a modest increased risk was observed among radiological technologists and technicians in the ODSS, a small group with only 10 cases.
Figure 1. Risk of colorectal cancer diagnosis among workers employed in each industry group relative to all others, Occupational Disease Surveillance System (ODSS), 2006-2016
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 colorectal cancer diagnosis among workers employed in each occupation group relative to all others, Occupational Disease Surveillance System (ODSS), 2006-2016
