Cancer incidence among Canadian Veterans: A matched cohort study.

Introduction: Occupational exposures related to military service may increase the risk of cancer for military Veterans, while high levels of fitness during service may decrease risk. However, few studies have compared this post-career cancer risk directly to the employed general population.

Methods: This retrospective cohort study used linked administrative data. Canadian Armed Forces and Royal Canadian Mounted Police Veterans in Ontario, Canada were matched 1:4 on age, sex, geography, and community-level income to a group of non-Veterans most likely to have been employed during a period similar to the Veterans' military service. Cancer diagnoses were identified using the Ontario Cancer Registry.

Results: During the study period, 642 of 30 576 included Veterans (2.1%) and 3408 of the 122 293 matched general population cohort (2.8%) experienced at least one cancer diagnosis. The crude rate of cancer was 153.5 per 100 000 person-years among Veterans vs. 205.9 per 100 000 person-years for the general population cohort. After adjusting for rurality and matching variables, Veterans had an 27% lower risk of developing any cancer than their matched comparators [hazard ratio = 0.73 (95% CI: 0.67-0.80)]. Among specific cancer types, the risk of lung and colorectal cancer was significantly lower for Veterans relative to the general population cohort; the risk of breast and prostate cancer was similar.

Discussion: This study adds to the growing international evidence suggesting that risk of many cancers among Veterans is lower or similar to the general population. Further understanding of the complex relationships among occupational exposures, environmental factors, and lifestyle factors is needed.