Section 750 of the FY2021 NDAA mandated a two-phase study on the incidence of cancer diagnosis and mortality among military fixed wing aviators (aircrew) and aviation support personnel (ground crew). Phase 1 required an epidemiologic study to determine if there was a higher rate of cancers and cancer mortality occurring for military aircrew and ground crew as compared to the US population using the Surveillance, Epidemiology, and End Results database. The Phase 1 study was performed by the Defense Health Agency’s Armed Forces Health Surveillance Division, in collaboration with the National Cancer Institute, North American Association of Central Cancer Registries, the Military Departments, And the Murtha Cancer Center at Walter Reed National Military Medical Center. Phase 1 was divided into Phase 1A and Phase 1B to account for all military branches, Active and Reserve Components, Veterans, and National Guard service members.

There were 156,050 aircrew and 737,891 ground crew included and followed in the Phase 1A study and 138,505 aircrew and 659,825 ground crew included and followed in the Phase 1B study between 1992 and 2017. Military members from all services were included.

The Phase 1A study was conducted between July 2021 and April 2022. The Phase 1B study was conducted between April 2022 and March 2024.

The Phase 2 study is required to investigate and identify the specific occupational and environmental risk factors associated with the increased risk of the cancers identified in the Phase 1 study. The Phase 2 study will aim to closely examine several dimensions of risk, including:

• Identifying potential carcinogenic toxicants, hazardous materials, and radiation exposures associated with military aviation activities;
• Differences in the overall health and mortality rates of the military population compared to the general population, supplementing results from Phase 1A and 1B studies;
• Specific duties, types of aircraft, and dates and locations of service associated with higher incidences;
• Latency, exposure lags, and other temporal factors related to cancer including duration of service, and age at first and last service, which may inform cancer screening guidelines.

Both aircrew and ground crew members had lower cancer mortality rates when compared to the U.S. population. However, incidence rates of some cancers were found to be higher than the U.S. population.

Compared to the U.S. population, aircrew had a:

• 75-87% higher rate of melanoma,
• 31-39% higher rate of thyroid cancer,
• 16-20% higher rate of prostate cancer, and a
• 15-24% higher rate of cancer for all sites combined.

In Phase 1A, ground crew members had a:

• 19% higher rate of brain and nervous system cancer,
• 15% higher rate of thyroid cancer,
• 9% higher rate of kidney and renal pelvis cancer,
• 9% higher rate of melanoma, and
• 3% higher rate of cancers for all sites combined.

In Phase 1B, ground crew had a 12% higher rate of kidney and renal pelvis cancer. Rates of other site-specific cancers were either similar to or less than the U.S. population.

The FY2021 NDAA Sec. 750 requires a Phase 2 study since the Phase 1A and 1B studies found an increased rate of some cancers among military aircrew or ground crew compared to the U.S. population.

The current data is not sufficient to determine a link between military occupations and cancer. The Phase 1A and 1B studies showed higher rates of cancer diagnoses in military aviators and ground support personnel than in the U.S. population when matched for age, race, and sex. However, these findings cannot determine whether military occupations and cancers are linked. The purpose of the Phase 2 study will look at military occupational exposures and cancers.

Phase 1B captured the National Guard and Reserve service members by obtaining data from the Department of Veterans Affairs Central Cancer Registry (VACCR) and 41 state cancer registries.

The study did not include members of the Coast Guard due to the small number of fixed wing aviators and limited outpatient clinical data available to provide reliable analysis and interpretation.

The concerns about cancer incidence in specific sub-groups such as the USAF C2ISR community are important, however, MACS is looking at the larger community of aircrew and groundcrew across the DOD. Phase 2 of the MACS will look at some of the specific concerns raised by the community such as exposure to non-ionizing radiation. Notably, the inclusion of larger populations with similar exposures to the USAF C2ISR community provides increased statistical power to detect factors that might increase cancer risk.

Yes, the Phase 1B study included additional data from the Department of Veterans Affairs Central Cancer Registry (VACCR), which resulted in a better understanding of cancer cases of veterans.

Yes, but previous studies have primarily focused on U.S. Air Force aviators. Our study is one of the largest to date and includes aviators from the Army, Navy, Air Force, and Marine Corps.

If the weight of evidence is consistent with there being a causal effect of military occupations and cancer rates, the DoD will engage evidence-based mitigation measures. Contributions to the scientific literature from the ongoing MACS will help design better studies for the aviation community in the future. The results from MACS Phase 2 will inform the design of any potential follow-on epidemiologic studies looking at specific aviation communities, such as the USAF C2ISR community.

The MACS Phase 2 study, is being conducted by the National Institute for Occupational Safety and Health, part of the Centers of Disease Control and Prevention, an organization with extensive experience evaluating aircrews and the aviation environment. Phase 2 is expected to start in the early part of FY 2025 and conclude in FY 2029.

A recent study from the Millennium Cohort Study, published in March 2023, found a lower rate of cancer mortality in deployed military members, referred to as the “healthy deployer affect.”

Contact the Armed Forces Health Surveillance Division at dha.ncr.health-surv.mbx.webmaster@health.mil.