made based on review of primary studies. Confidence in a secondary study is substantially reduced if the statistical analysis did not include adjustment for confounders, if the data were obtained from self-reported cross-sectional surveys or from screening instruments that relied solely on self-reports of diagnoses, or if response rates were unacceptably low. Without supportive evidence from primary studies, the potential for unreliable findings due to bias, chance, or multiple comparisons may outweigh the extent to which secondary studies may contribute, even collectively, to the overall conclusion of the committee about an association between deployment and any specific health outcome. Understanding the relationship between a health outcome and deployment may also be hampered by attempts to identify specific harmful exposures based on recall many years after the war. Virtually none of the studies verified veterans’ reported exposures against military records.
This chapter excludes studies of participants in Gulf War registries established by the Department of Veterans Affairs (VA) or the Department of Defense (DoD), which were not intended to be representative of the population of Gulf War veterans. Registry participants cannot be considered representative of all Gulf War veterans in that they are self-selected, and many may have joined the registries because they believed that they have symptoms of a new medical syndrome; they were not a random sample of Gulf War military personnel, and there is no nondeployed comparison group.
Cancer can develop at any age but about 77% of cancers are diagnosed in people aged 55 and older. Furthermore, cancer is a disease of long latency, meaning that often the diagnosis of a cancer does not occur until 15 to 20 years or longer after the exposure that caused it (Cogliano et al., 2004). Therefore, many veterans are still young for cancer diagnoses (the mean age of military personnel during the Gulf War was 28), and for most cancers, the time since the Gulf War is probably too short to expect to observe the onset of cancer. Cancers with younger average age at onset, and also possible shorter latency periods, can include testicular cancer, skin cancer, leukemias and lymphomas, and brain cancer.
The majority of observations on the association of overall and cause-specific cancers (that is, malignant neoplasms) with Gulf War deployment are discussed in studies of general mortality and hospitalizations, rather than in reports focused specifically on cancer. However, a few studies on brain and testicular cancer in Gulf War veterans have been published. All studies in which malignant neoplasms, as a group or at particular sites, are specifically identified are reviewed here and summarized in Table 4-1.
The Volume 4 committee identified one cohort mortality study assessing the relationship between nerve-agent exposure caused by weapons demolition at Khamisiyah with brain cancer deaths in US Gulf War veterans. Bullman et al. (2005) explored the relationship between estimated exposure to chemical munitions destruction (sarin gas) at Khamisiyah in 1991 with cause-specific mortality of Gulf War veterans through December 31, 2000. Using the DoD’s 2000 sarin plume exposure model (Rostker, 2000), 100,487 military personnel were identified as potentially exposed and 224,980 similarly deployed military personnel were considered