Cholangiocarcinoma (CCA) mortality in Vietnam war era veterans

There is concern about the risk of cholangiocarcinoma mortality (CCA) among U.S. veterans who deployed to the Vietnam War theater. A variety of risk factors potentially related to Vietnam deployment may be associated with an increased risk of mortality from CCA. This study assessed the risk of CCA mortality among all Vietnam War era veterans, the first study to do so.

The Vietnam Era Veterans Mortality Study is a retrospective mortality study of all 2.5 million veterans who served in Vietnam and Southeast Asia (theater) and the 7.3 million veterans who served elsewhere during the Vietnam War (non-theater). Mortality was followed from 1979 to 2019. Hazard ratios (HRs) calculated from Cox proportional hazards models, adjusted for sex and age, compared CCA mortality risk between theater and non-theater veterans overall and by branch of service. Branch specific crude rates of CCA were also compared between theater and non-theater veterans.

There were 2410 and 6502 CCA deaths among all theater and non-theater veterans respectively. Overall, there was no increased CCA mortality risk among theater versus non-theater veterans after adjusting for sex and age (hazard ratio, (HR: 1.00, 95 % CI: 0.95-1.04). When stratified by branch, the crude HRs for CCA were no different between branch-theater status groups except in non-theater Marines who had lower risk. A monotonic increase in crude rates for CCA mortality was observed in both theater and non-theater over forty years of follow-up.

There was no increased risk of CCA mortality in theater versus non-theater U.S. Vietnam War veterans, an important and new finding. This study lacked data on environmental exposures and behavioral factors that would further inform analyses of CCA risk. Identification of Vietnam era veterans' specific risk factors for CCA would require alternate methods and data which do not exist.