Cancer Risk in Veterans Enlisted in the United States Military after September 11, 2001: A Retrospective Cohort Study

Potential exposures to toxicants during military deployment may increase the risk of developing cancer. This study was undertaken to determine whether there is an association of cancer risk with post-9/11 deployment.

This is a cohort study of U.S. veterans who enlisted in the military after September 11, 2001, and enrolled in the Veteran Affairs (VA). The primary outcome was incident cases of cancer. Deployment was determined by identification on the Operation Enduring Freedom and Operation Iraqi Freedom roster managed by the VA and Department of Defense. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to measure risk of the outcome associated with the exposure in a logistic regression model adjusted for sex, race and ethnicity, and age at enlistment. To assess potential effect measure modification, analyses were stratified by branch of military and rank. Institutional Review Board approval and a waiver of consent were obtained.

There were 1,777,583 veterans who met inclusion criteria: 832,897 (47%) deployed and 944,686 (53%) nondeployed. Among deployed and nondeployed, a total of 3,986 and 2,885 veterans developed cancer, respectively. Deployed veterans had a higher risk of developing transitional cell carcinoma (OR 1.19; 95% CI 1.01-1.39, P = 0.03), head and neck cancer (OR 1.17; 95% CI 1.02-1.35, P = 0.03), and breast cancer (in females) (OR 1.13; 95% CI 1.00-1.27, P = 0.04) compared to nondeployed veterans.

Post-9/11 deployment was associated with a modest increased risk of specific cancers. However, analyses were limited by the incomplete nature of retrospective data, including the lack of details on specific toxicants and potential confounders. Our findings underscore the need for prospective and comprehensive documentation of military exposures.