2 Mortality and Cancer Incidence Study
2.1
Introduction
The baseline Australian Gulf War veterans Health Study included a Mortality and Cancer
Incidence Cohort Study. In 2002, the cohort was linked to records held in the Australian
National Death Index (NDI) to determine all-cause mortality in the cohort for the period 1
January 1991 to 31 December 2000, and to the Australian Cancer Database (ACD) to
determine cancer-incidence rates in the cohort for the period 1 January 1991 to 31
December 1998. The matching revealed a total of 43 deaths and 19 cancers among male
cohort members in the study period. Although the rate of death and the rate of cancer were
both slightly higher in the Gulf War veteran group than in the comparison group, these
differences did not reach statistical significance. However, the cohort was relatively small in
size, the members were relatively young and the period of follow up was short, all limiting the
power of the study to detect excess mortality and cancer at that time. Using the same cohort
as that used in the 2002 linkage, the follow up Australian Gulf War veterans Health Study
includes a repeat investigation of mortality and cancer incidence.
2.2
Aim
The aim of these analyses was to investigate whether Gulf War veterans have an excess
risk of death or of developing cancer, than the comparison group or the Australian
community.
2.3




Research questions
Do Gulf War veterans have a greater rate of death than the comparison group?
Do Gulf War veterans have a greater rate of death than same-aged Australians?
Do Gulf War veterans have a greater risk of developing cancer than the comparison group?
Do Gulf War veterans have a greater risk of developing cancer than same-aged Australians?
Cohort composition
At the commencement of the baseline Australian Gulf War veterans’ Health Study, a cohort
totalling 4,975 members was compiled which consisted of the entire deployed group of 1,871
Australian veterans of the Gulf War and 2,924 comparison group members. The Australian
Gulf War veterans were defined as ADF members who deployed in support of the Gulf War
at any time during the period 2 August 1990 to 4 September 1991 as part of ADF Operation
Ozone or Operation Damask, or with overseas forces as part of Operations Desert Shield or
Australian Gulf War Veterans’ Follow Up Health Study: Technical Report 2015
Page 5
Desert Storm. They were primarily Naval personnel (84%) and men (98%). Comparison
group members were randomly drawn from a population of 26,411 ADF personal who were
in operational units at the time of the Gulf War but who were not deployed to that conflict.
The comparison group was frequency matched to the Gulf War veteran group by sex, 3-year
age band, service branch (Royal Australian Navy, Australian Army, Royal Australian Air
Force), 2-rank categories (Officer versus other ranks) for Army personnel, and 2-task
categories (aircrew versus non-aircrew) for the Air Force. There was some oversampling of
eligible Army and Air Force comparison group members because the total numbers in these
service branches were very low relative to the Navy, and a lower participation rate was
anticipated in the comparison group relative to the Gulf War veterans’ group. Further details
regarding the eligibility criteria for each study group are shown in Appendix 2.
The cohort for the Mortality and Cancer Incidence Study, in 2002 and again at follow up,
comprised 4,793 members. This was the entire original cohort minus two comparison group
members who, during the baseline Health study, declined to participate in the Mortality and
Cancer Incidence Study.
Registry linkage
Approval for both the NDI and ACD linkage was obtained from the Human Research Ethics
Committees representing the AIHW, Monash University, the ADF and DVA. Additional
approvals for the ACD linkage were obtained from the each of the Human Research Ethics
Committees representing the Australian State and Territory cancer registries respectively.
In July 2011 a dataset, including the full name, date of birth, last known state and last
contact date for the cohort members, was provided to the AIHW for linkage to the NDI and
the ACD. At the time of the linkage, the NDI was complete up to 30 November 2010 and the
ACD was complete up to 31 December 2008.
Data returned from the NDI included the identifying information (e.g. full name and date of
birth) for the NDI record that appeared to match a cohort member, and also date of death
and all causes of death coded in International Classification of Diseases (ICD) Version 10
and ICD Version 9 codes. Returned matches were independently reviewed by two members
of the Monash research team to identify those to be accepted as likely true matches.
Data returned from the ACD included identifying information for the ACD record that
appeared to match a cohort member in the case that the cohort member had participated in
the cross-sectional component of the baseline Gulf War veterans Health Study. For cohort
Australian Gulf War Veterans’ Follow Up Health Study: Technical Report 2015
Page 6
members who had not participated in the cross-sectional component of the baseline Gulf
War veterans Health Study, data returned for matches to the ACD were deidentified. Other
ACD data included for all matches included date of cancer diagnosis, site of body
(topography), histology (affected tissue type), state in which the cancer was diagnosed, date
of death (if applicable) and the ICD-10 codes for the type of cancer.
Statistical analysis
The cohort was followed-up from 1st January 1991 to 30th of November 2010 for mortality
and 31st of December 2008 for cancer incidence. These periods were used to calculate total
person-time.
Data were analysed using Stata Version 12 and a 5% level of significance was used in
interpreting statistical significance. Box 1 describes the ICD 10 and ICD 9 codes used for
each classification of cause of death and cancer type.
Box 1 Codes used to categorise causes of death and types of cancer.
Causes of Death [ICD9; ICD10 codes]
Types of cancer [ICD9; ICD10 codes]
All-cause [001-999;A00-Y99]
All malignant neoplasms [C00-C97;D45-
Cancer [140-239; C00-D48]
D46;
Cardiovascular diseases [390-459; I00-I99]
Lip cancer [C00]
All External causes [800-999; V01-Y98]
Colorectal [C18-C20]
Intentional self-harm [950-959; X60-X84]
Other digestive organs [C15 - C17; C21-
Transport accidents [800-848; V01-V99]
C26]
D47.1; D47.3]
Lung, trachea and bronchus [C33-C34]
Melanoma [C43]
Prostate [C61]
Testis [C62]
Kidney [C64]
Brain and other CNS cancers [C70-C72]
Thyroid [C73]
All lymphomas [C81-C85; C88; C90-C91]
Leukemia [C91-C95]
For comparison with Australian population rates, cancer and death data for the general
Australian population were obtained from AIHW. Using the population rates, expected
number of deaths or cancer cases were calculated for each age group and calendar year of
follow-up. The expected numbers of deaths or cancers were then compared with the cohort
Australian Gulf War Veterans’ Follow Up Health Study: Technical Report 2015
Page 7
observed numbers to calculate Standardised Mortality Ratios (SMRs) and Standardised
Incidence Ratios (SIRs). In keeping with usual practice, and for ease of presentation, the
SMRs and the SIRs and their 95% confidence intervals were multiplied by 100. Values over
100 represent increased risk of death or cancer and values below 100 represent decreased
risk of death or cancer. A value of 100 is where the risk of death or cancer is the same as
that in the Australian population.
The rate of death or cancer in the Gulf War veteran group was compared with the rate of
death or cancer in the comparison group of the cohort using hazard ratios (HRs). Hazard
ratios were calculated using the Cox regression model.22 The hazard ratios were adjusted
(adj HR) for branch of service (Navy; Army; Air Force), rank (Commissioned Officer (CO);
non-commissioned officer (NCO); other ranks) and age (<20; 20-24; 25-34; >=35 years),
each estimated as at August 1990, the approximate commencement date of the Gulf War.
2.4
Results
Because of the very small proportion of women in the cohort (approximately 2%) results for
the 4,680 men in the cohort (1,833 Gulf War veterans and 2,847 comparison group) are
presented in the tables in this chapter. There were no female deaths in either group
identified during the NDI linkage over the study period. A total of four cancers, all breast
cancers, were identified for females from the ACD linkage during the study period. These
four cancers were all among members of the comparison group.
Men in the cohort averaged 47.7 years of age (sd 6.38) at 30 November 2010 (the date to
which mortality data was available). A breakdown of the cohort into age category at 30
November 2010, service branch at the time of the Gulf War and rank at the time of the Gulf
War is shown in Table 1 for each study group. The Gulf War veteran group had a similar
age and rank composition to the comparison group. There were proportionately fewer Army
and Air Force members in the Gulf War veteran group, reflecting some over-sampling for
these service branches in the comparison group.
Australian Gulf War Veterans’ Follow Up Health Study: Technical Report 2015
Page 8
Cohort characteristics
Table 1 Demographic characteristics for the male members of the cohort
Characteristic
Gulf War veterans
Comparison group
Whole cohort
N=1,833
N=2,847
N=4,680
n (%)
n (%)
n (%)
35 – 44
742 (40.5)
1,083 (38.0)
1,825 (39.0)
45 – 54
863 (47.1)
1,368 (48.1)
2,231 (47.7)
55+
228 (12.4)
396 (13.9)
624 (13.3)
Expected age in years at
30 November 2010
between groups p-value = 0.16
Service branch at August 1990
Navy
1,558 (85.0)
2,088 (73.3)
3,646 (77.9)
Army
115 (6.3)
319 (11.2)
434 (9.3)
Air Force
160 (8.7)
441 (15.5)
600 (12.8)
between groups p-value <0.001
Rank at August 1990
Officer
Non-commissioned Officer
Enlisted rank
405 (22.1)
720 (25.3)
1,125 (24.0)
1,168 (63.7)
1,676 (58.9)
2,844 (60.8)
260 (14.2)
451 (15.8)
711 (15.2)
between groups p-value = 0.004
Mortality
The number of deaths observed in each study group, and the number expected in the
Australian population of same-aged men, are shown in Table 2 for the period 1 January
1991 to 30 November 2010. In total 108 deaths were observed, comprising 2.3% of the
cohort. There were 49 deaths in the Gulf War veteran group and 59 deaths in the
comparison group. In both study groups the all-cause mortality was lower than that in the
Australian male population however this difference was statistically significant only for the
comparison group (all cause SMR=59, 95% CI 45-76), while it did not quite reach statistical
significance for the Gulf War veterans (all cause SMR=77, 95% CI 58-102). Mortality from
all-external causes was also statistically significantly lower in the comparison group than in
the same-aged Australian male population. There were no significant differences between
the Gulf War veterans and the Australian male population, and between the comparison
group and the Australian male population, for all other causes of death.
Australian Gulf War Veterans’ Follow Up Health Study: Technical Report 2015
Page 9
Table 2 Mortality rates for the Gulf War veterans and comparison group relative to the
Australian male population
Gulf War veterans
person years = 36,065.1
N = 1,833
Cause of death
Comparison group
person years = 56,139.1
N = 2,847
Observed
Expected
SMR (95% CI)
Observed
Expected
SMR (95% CI)
All-cause
49
63.7
77 (58–102)
59
100.8
59 (45–76)
Cancer
16
14.0
115 (70–187)
14
22.6
62 (37–104)
Cardiovascular
diseases
5
10.8
46 (19–111)
11
17.5
63 (35–114)
All External
causes
17
24.3
70 (43–113)
23
37.5
61 (41–92)
Intentional selfharm
6
9.9
60 (27–134)
9
15.4
59 (30–113)
Transport
accidents
7
6.4
110 (52–231)
10
9.8
103 (55–191)
Table 3 shows the number of deaths in each study group, as a proportion of group size, and
the ratio of deaths in the Gulf War veteran group relative to those in the comparison group.
There were no statistically significant differences in mortality rates between the Gulf War
veterans and the comparison group. It is worth noting that deaths from intentional self-harm
were very similar in the two groups. However, there was an overall pattern of the adjusted
HRs for all deaths and all causes of death (except for deaths from cardiovascular disease)
being slightly greater in the Gulf War veteran group.
Table 3 Mortality rates for the Gulf War veterans relative to the comparison group
Gulf War veterans
Comparison group
N = 1,833
N=2,847
Cause of death
n
(%)
n
(%)
Adj HR (95% CI)
All causes of death
49
(2.7)
59
(2.1)
137 (94 – 202)
Cancer
16
(0.9)
14
(0.5)
182 (88 – 374)
Cardiovascular diseases
5
(0.3)
11
(0.4)
79 (27 – 229)
All External causes
17
(0.9)
23
(0.8)
119 (63 – 225)
Intentional self-harm
6
(0.3)
9
(0.3)
112 (39 – 317)
Transport accidents
7
(0.4)
10
(0.4)
119 (45 – 316)
Cancer incidence
The number of cancers observed in each study group, and the number expected in the
Australian population of same-age men, are shown in Table 4 for the period 1 January 1991
to 30 December 2008. In total 115 cancers were observed, affecting about 2.5% of the total
male cohort; 49 (2.6%) in the Gulf War veteran group and 66 (2.3%) in the comparison
Australian Gulf War Veterans’ Follow Up Health Study: Technical Report 2015
Page 10
group. In both study groups cancer incidence from all-causes, and from the specific causes
tabulated, were not statistically significantly different from those in the same aged Australian
male population, apart from a significant excess of thyroid cancer in the comparison group.
The other finding of note is the higher than expected number for brain cancers in the Gulf
War veterans, although this did not reach statistical significance and was based on very
small numbers.
Table 4 Cancer incidence rates for the Gulf War veterans and comparison group relative to the
Australian male population
Gulf War veterans
person years = 32,664.7
N = 1,833
Cancer type
Comparison group
person years = 50,797.7
N = 2,847
Observed
Expected
SIR (95% CI)
Observed
Expected
SIR (95% CI)
All malignant
neoplasms
49
49.4
99 (76-133)
66
79.4
83 (65-107)
Colorectal
**
4.5
89 (33-237)
7
7.3
95 (45-200)
Other digestive
organs
6
3.3
184 (83-410)
5
5.3
94 (39-226)
Brain and other
CNS cancers
**
1.7
238 (89-635)
**
2.7
38 (53-267)
Melanoma
11
10.8
102 (56-184)
14
17.2
81 (48-137)
Prostate
8
5.0
161 (81-323)
6
8.3
73 (33-161)
Testis
**
3.9
52 (13-207)
**
5.9
34 (8-135)
Kidney
**
1.7
58 (8-414)
5
2.8
179 (75-431)
Thyroid
**
1.1
91 (13-647)
5
1.7
289 (120-693)
Lung, trachea and
bronchus
All lymphomas
**
2.4
42 (6-300)
**
3.9
52 (13-207)
**
5.1
39 (10-156)
8
8.2
98 (49-196)
Leukaemia
**
1.7
59 (8-420)
**
2.7
149 (56-397)
Lip cancer
**
1.7
173 (56-537)
**
2.8
109 (35-338)
Other cancer
types
6
8.2
73 (33-163)
8
13.2
61 (30-122)
** Observed number of cancer not displayed because of small numbers (<5 cases).
Table 5 shows the ratio of incident cancers in the Gulf War veteran group relative to those in
the comparison group. There were no statistically significant difference in the overall cancer
incidence rates between the Gulf War veterans and the comparison group. While none of
the specific cancer types were found to be statistically significantly higher in the Gulf War
veterans, there were some types of cancer (e.g. brain and prostate) where the Adj HR was
greatly in excess of one, but the confidence intervals were very wide because of small
numbers.
Australian Gulf War Veterans’ Follow Up Health Study: Technical Report 2015
Page 11
Table 5 Cancer incidence rates for the Gulf War veterans relative to the comparison group
Gulf War veterans
N = 1,833
Cancer type
Comparison group
N=2,847
n
(%)
n
(%)
Adj HR (95% CI)
All malignant neoplasms
49
(2.7)
66
(2.3)
120 (83–173)
Colorectal cancer
**
7
(0.2)
92 (28–308)
Other digestive organs
6
5
(0.2)
169 (50–571)
Brain
**
Melanoma
11
(0.6)
14
(0.5)
119 (54–262)
Prostate
8
(0.4)
6
(0.2)
209 (72–603)
Testis
**
(0.3)
**
513 (67–3924)
**
170 (27–1078)
** Observed and expected values not displayed because of small numbers (<5 cases).
2.5
Key findings
In the 20 year period since the Gulf War, there have been proportionately fewer deaths in
the male Gulf War veteran group compared to the same aged Australian male population,
and, while not quite reaching statistical significance, slightly more overall deaths and deaths
from cancer occurred in the male Gulf War veteran group relative to the comparison group.
In the same time period, mortality from all-external causes, has been statistically significantly
lower in the male comparison group than in the same aged Australian male population.
In the 18 year period since the Gulf War, there have been no statistically significant
differences in cancer incidence of any type between the male Gulf War veterans, the male
comparison group members and the same-aged Australian male population.
While the results were suggestive of some types of cancer (eg brain and prostate) being
higher than expected among the Gulf War veterans when compared with the comparison
group, these were based on very small numbers and therefore the possibility of these
findings being observed by chance could not be excluded in the current analysis.
There were too few deaths or cancers among females in the study group to make any
meaningful interpretation.
The power of the study to detect excess mortality and cancer continues to be limited by the
fact that the cohort was still quite young at 30 November 2010, with approximately 40% aged
between 35-44 years, and the period of follow up is still relatively short for the purpose of
detecting disease-related deaths or cancers of long-latency.
Australian Gulf War Veterans’ Follow Up Health Study: Technical Report 2015
Page 12