Cancer
The impact of cancer of Indigenous people often attracts much less attention than it deserves, for two main reasons. First, the level of identification of Indigenous people in cancer notifications is known to be poor, with only the data from Queensland, WA, SA, and the NT deemed adequate for publication (see below).
Second, the fact that cancer has often been reported in terms of the proportions of deaths it causes, rather than by rates, has tended to give the erroneous impression that cancer does not have a great impact among Indigenous people. Proper analyses, however, suggest that there are around 40% more cancer deaths among Indigenous Australians than expected on the basis of non-Indigenous rates [1].
Extent of cancer among Indigenous people
The evidence available suggests that the incidence rates of cancer for Indigenous people are slightly lower than those for non-Indigenous people, but that death rates are generally higher, as reflected in the Indigenous to non-Indigenous rate ratios (Table 1) [2-6].
Table 1 Indigenous to non-Indigenous standardised cancer incidence and death rate ratios, selected jurisdictions, by sex, Australia, various years
| Jurisdiction | Incidence rate ratio | Death rate ratio | ||
| Male | Female | Male | Female | |
| Queensland | 0.8 | 0.9 | 1.7 | 1.6 |
| Western Australia | 0.6 | 0.7 | 1.3 | 1.2 |
| South Australia | 0.4 | 0.5 | 0.9 | 1.3 |
| Northern Territory | 0.9 | 1.0 | 1.1 | 1.3 |
Source: ABS & AIHW, 2003 [7]; ABS & AIHW, 2005 [2]; Zhao, Condon and Garling, 2004 [6]
Notes:
1. Incidence data are for 1997-2001; mortality data are for 1999-2001
2. Rate ratio is the Indigenous age-standardised rate divided by the non-Indigenous age-standardised rate
3. Caution should be exercised in the interpretation of these rate ratios because of the known levels of under-identification of Indigenous status in death registrations and the unknown levels of under-identification in cancer registrations (except for the NT where a correction factor of 15% is indicated)
The differences between Indigenous and non-Indigenous people in incidence rates are likely to be much less than suggested by these rate ratios, however, because of the under-identification of Indigenous people in cancer registrations [2, 8]. Adjustment for the estimated under-identification of 15% in cancer registrations in the NT suggests Indigenous to non-Indigenous incidence rate ratios of 1.0 and 1.1 respectively for males and females in that jurisdiction. The levels of under-identification in cancer registrations are not known for Queensland, WA and SA, but special analysis of cancer incidence among Indigenous people living in SA in 1977-2001 found that the Indigenous and non-Indigenous rates for that State were similar – the rate ratio for males was estimated at 0.9 and that for females at 1.0 [9].
The under-identification of Indigenous people in deaths registrations means that the differences between Indigenous and non-Indigenous people in cancer death rates are likely to greater than suggested by the rate ratios listed in Table 1, particularly for Queensland and, to a lesser extent, WA and SA [2].
The patterns of cancer differ somewhat between jurisdictions, but, overall in 1997-2001, lung cancer was the most common specific cancer for Indigenous males and the second most common, after breast cancer, for Indigenous females [2]. The next most common cancers for Indigenous males were prostate cancer, colorectal cancer, cancer of an unknown primary site, and liver cancer, and for Indigenous females cervical cancer, colorectal cancer, colorectal cancer and cancer of the uterus.
Lung cancer was responsible in 1999-2003 for 32% of Indigenous male deaths from cancer and for 21% of Indigenous female deaths from cancer. Cancers of the digestive organs were responsible for 29% of Indigenous male deaths from cancer and for 19% of Indigenous female deaths from cancer [2].
The greater differences between Indigenous and non-Indigenous people in death rates than in incidence rates could reflect a higher proportion among Indigenous people than among non-Indigenous people of cancers with high case-fatality rates, a generally more advanced stage of cancer at time of diagnosis or differences in treatment outcomes by stage of cancer at diagnosis.
Indigenous people do experience ‘more than their share’ of cancers with poorer survival, including cancers of the lung, liver, pancreas, oropharynx and oesophagus [9, 10].
A detailed analysis undertaken by the SA Cancer Registry of cancer among people living in that State in 1988–1994 concluded that the higher death rates among the Indigenous population were due to the more advanced stage of the tumours at diagnosis and a lower survival for primary cancers matched by site, age at diagnosis, sex, year of diagnosis and, where possible, histological type [11].
Broadly similar conclusions were reached from an analysis of the survival of NT residents diagnosed with cancer in 1991-2000 with the notable exception that Indigenous people with lung cancer were diagnosed at an earlier stage than were non-Indigenous people [3].
Similar findings were also reported from a matched cohort study of 815 Indigenous and 810 non-Indigenous people living in Queensland and diagnosed with cancer in 1997-2002 – the likelihood of death from cancer was 30% higher for Indigenous cases than for non-Indigenous cases after accounting for cancer stage at diagnosis, treatment, and the higher rates of co-morbidities (such as diabetes, chronic renal disease, respiratory disease and acute coronary conditions) existing among Indigenous cases [12].
Importantly, analyses of cancer and cancer services for Indigenous people in the NT have highlighted the fact that the absolute differences in survival after diagnosis with cancer are greatest for cancers with the highest survival in non-Indigenous people [4, 13]. That is, for cancers that are ‘amenable to early diagnosis, effective treatment and a high probability of cure’ [13, p.8]. As well, some of the most common cancers among Indigenous people are preventable, such as ‘through reduced tobacco consumption, increased Pap test coverage and follow-up treatment, hepatitis B immunisation, and reduced alcohol misuse’ [13, p.9] (Hepatitis B is the main risk factor for primary liver cancer.)
The review concluded that ‘the experience of Indigenous people and cancer provides evidence that the Australian health system is not operating as effectively for Indigenous people as for other Australians’ and that there was a need for ‘strengthening primary health care services, reducing barriers for access to specialist services and improving collaboration between the two’ [13, pp. 16-17].
References
1 Cunningham J, Paradies Y (2000) Mortality of Aboriginal and Torres Strait Islander Australians, 1997: occasional paper. (ABS catalogue no. 3315.0) Canberra: Australian Bureau of Statistics
2 Australian Bureau of Statistics, Australian Institute of Health and Welfare (2005) The health and welfare of Australia's Aboriginal and Torres Strait Islander peoples 2005. (ABS catalogue no. 4704.0) Canberra: Australian Institute of Health and Welfare and the Australian Bureau of Statistics
3 Condon JR, Armstrong BK, Barnes T, Zhao Y (2005) Cancer incidence and survival for Indigenous Australians in the Northern Territory. Australian and New Zealand Journal of Public Health;29(2):123-128
4 Condon JR, Barnes T, Cunningham J, Armstrong BK (2004) Long-term trends in cancer mortality for Indigenous Australians in the Northern Territory. Medical Journal of Austalia;180(10):504-511
5 Kirov E, Francis J, Thomson N(2003) Cancer. In: Thomson N, ed. The health of Indigenous Australians. South Melbourne: Oxford University Press:207-223
6 Zhao Y, Condon JR, Garling LS (2004) Cancer incidence and mortality, Northern Territory 1991-2001. Darwin, NT: Department of Health and Community Services
7 Australian Bureau of Statistics, Australian Institute of Health and Welfare (2003) The health and welfare of Australia's Aboriginal and Torres Strait Islander peoples 2003. (ABS Cat no.4704.0, AIHW Cat no. IHW11) Canberra: Australian Bureau of Statistics
8 Condon JR, Zhao Y, Armstrong BK, Barnes A (2004) Northern Territory Cancer Register, data quality 1981-2001. Darwin: Department of Health and Community Services
9 Roder D (2005) Comparative cancer incidence, mortality and survival in Indigenous and non-Indigenous residents of South Australia and the Northern Territory. Cancer Forum;29(1):7-9
10 Lowenthal RM, Grogan PB, Kerrins ET (2005) Reducing the impact of cancer in Indigenous communities: ways forward [conference report]. Medical Journal of Australia;182(3):105-106
11 South Australian Cancer Registry (1997) Epidemiology of cancer in South Australia. Adelaide: South Australian Cancer Registry
12 Valery PC, Coory M, Stirling J, Green AC (2006) Cancer diagnosis, treatment, and survival in Indigenous and non-Indigenous Australians: a matched cohort study. The Lancet;367(9525):1842-1848
13 Condon J (2004) Cancer, health services and Indigenous Australians. (Consultant report no.5) Canberra: Office for Aboriginal and Torres Strait Islander Health
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