DOD Aviation Cancer Study: Phase 1B Confirms Higher Cancer Rates
In February 2023, the Department of Defense (DOD) released the initial Phase 1A results of a significant study on military aviation cancer rates. This study, titled “Study on the Incidence of Cancer Diagnosis and Mortality among Military Aviators and Aviation Support Personnel,” was mandated by section 750 of the William M. (Mac) Thornberry National Defense Authorization Act (NDAA) for Fiscal Year 2021 (Public Law 116–283). The study aimed to investigate cancer incidence and mortality among military fixed-wing aviators (aircrew) and aviation support personnel (ground crew).
Covering data from 1992 to 2017, the Phase 1A results revealed a 24% higher rate of cancer across all sites in aircrew and a 3% higher rate of cancer across all sites in ground crew compared to the general US population. However, the Phase 1A study had notable gaps and limitations, particularly regarding the lack of cancer data on veterans and members of the Reserve and National Guard.
To address these gaps, a supplementary Phase 1B study was conducted that included data from the Department of Veterans Affairs (VA) and 41 state cancer registries, providing a more comprehensive analysis of cancer rates among military personnel. Released to Congress in May of 2024, the Phase 1B report’s findings for aircrew members are consistent with findings from the Phase 1A report.
Phase 1B Study Findings:
Compared to a demographically similar U.S. population, aircrew had a combined 15 percent higher rate of cancer for all sites, including a 75 percent higher rate of melanoma, 31 percent higher rate of thyroid cancer, and 20 percent higher rate of prostate cancer.
Ground crew members had a combined 5 percent lower rate of all sites, including a 12 percent higher rate of kidney and renal pelvis cancer, compared to the demographically similar U.S. population.
The median age at diagnosis for malignant cancer of all sites was 55 years in aircrew and 54 years in ground crew. In contrast, the median age at diagnosis for malignant cancer of all sites was 67 years in the reference U.S. population.
Study Strengths:
One of the largest and most comprehensive studies of military aircrew and ground crew cancer risks.
Sufficient representation of women in the study population for evaluating female-specific cancers.
Inclusion of VA and state cancer registry data, which allowed better ascertainment of cases for Reserve and Guard members, as well as veterans.
Study Limitations:
Unable to identify an electronic data source containing information on military occupation and dates of service prior to 1990.
Outpatient data not available until 1996
Data in the DoD, VA, and State cancer registries became available at different times throughout the 1990s. Therefore, cancer data prior to 1997 is considered incomplete.
Data from a handful of states were excluded from the Phase 1B study, including the majority of data from two of the states with the largest veteran populations: Texas and Florida.
At the time of the study, Minnesota, Vermont, South Dakota, Kansas, Nevada, and Washington, D.C., were not participating in the VPR-CLS (Virtual Pooled Registry Cancer Linkage System). In addition, cancer registry data for Washington State did not include regions outside of Seattle/Puget Sound. Mississippi, Missouri, Texas, and Nebraska participated in the VPR-CLS but were excluded because they did not provide data prior to the deadline for this report.
Two-thirds of cancer cases from Florida were missing from the analysis because of State-specific rules about the release of data.
Takeaways:
The findings of higher rates of melanoma, prostate, and thyroid cancer among aircrew is consistent with findings from the Phase 1A report.
Findings for ground crew may have differed from the Phase 1A report due to differences in the study population (e.g., inclusion of Reserve and Guard members, exclusions based on home of record, and increased years of follow-up). However, kidney and renal pelvis cancers were elevated among Active Component ground crew in both Phase 1A and Phase 1B.
The median age of a malignancy diagnosis for an aircrew member (55) and groundcrew member (54) were much lower compared to the US population (67) suggesting an earlier onset of cancers by 12-13 years. This age difference indicates potential disparities or differences in risk factors, environmental and occupational exposures, or screening practices between the two populations.
Although overall mortality rates are 56% lower for aircrew and 35% lower for groundcrew (Phase 1A), military aviation crew who lose their battle with cancer are passing away at a younger age, with a median age of 56-57, in contrast to the median age of 72 in the US population, marking a significant gap of 15-16 years in life expectancy. Furthermore, the median age difference between cancer diagnosis and death from cancer is 2 years, compared to 5 years in the US population, indicating a 60% shorter survival period. While lower mortality rates could be explained by increased medical screening and health of the younger military population (healthy soldier effect), the findings of shorter life expectancy and survival period for those diagnosed with cancer could also indicate insufficient follow-up time for progression to mortality, variability in cancer types and aggressiveness, delayed diagnosis and treatment, or differences in effectiveness of treatment regiments.
An analysis of cancer staging data and screening rates would prove insightful to better understand the increased risk of cancers and mortality trends identified in this study.
Moving Forward:
Given the findings of higher incidence for some cancers among aircrew and ground crew in the Phase 1A and Phase 1B studies, a Phase 2 study is required.
Phase 2 will investigate and identify the potential specific occupational and environmental risk factors that may be associated with the increased risk of the cancers identified in the Phase 1A and 1B studies.
The Phase 2 study will likely need to be conducted in several stages over a couple of years. It would be expected to start sometime in early 2025.
Read the full report here.