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What do we know about cancer among Indigenous people?

For more detailed information about cancer among Indigenous Australians view our Indigenous cancer web resource

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Please reference this document as:
Australian Indigenous HealthInfoNet (2007) Frequently asked questions: what do we know about cancer among Indigenous people? Retrieved [access date] http://www.healthinfonet.ecu.edu.au/html/html_keyfacts/faq/faq_specific_health/cancer.htm

 

What do we know about cancer among Indigenous people?

What is cancer? (November 2007)

Cancer is a term for diseases in which abnormal cells grow and divide without control. This is usually the result of damage to a number of regulatory mechanisms within the cell [1]. These damaged cells grow to form a tumour - an abnormal mass of tissue which can be cancerous or benign (non-cancerous). Unlike the cells in benign tumours, cancer cells can invade nearby tissues and spread via a process known as metastasis. Metastasis occurs when cells become detached from the initial tumour and are carried through the bloodstream and lymphatic system to other parts of the body [2]. This eventually interferes with the function of normal cells and can lead to the death of the patient [1].

There are over 100 different types of cancer, each with its own pattern of growth and spread [3]. While the risk factors for different cancers may be shared or unique, the cause may still be unknown [4, 5]. The risk factors for cancer that are known can be broadly divided into environmental and internal (host) factors. Environmental factors include chemicals, radiation and viruses [2]. Chemicals that have been identified as carcinogenic (cancerous) include tobacco smoke, alcohol (if consumed excessively) and asbestos, as well as certain industrial chemicals and medical drugs. Diet is also thought to initiate or promote various cancers [1, 5]. Internal or host factors include hormones, immune conditions and inherited mutations [2]. While some cancers, such as breast and colon cancer, are thought to have a strong 'familial predisposition', there is still no evidence that cancer is normally 'programmed' in the cells [6].

The frequency of cancer increases with age, with relatively few people acquiring cancer before the age of 30 years. This is partly because it can take many years to acquire the multiple abnormalities that generate cancer cells [1]. Furthermore, the probability of being exposed to the risk factors for cancer also increases with time [6].

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What do we know about the numbers of new cancer cases (incidence) and deaths from cancer among Indigenous people? (November 2007)

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) [7-11] . (The age-standardised rates shown in the Table have been adjusted for the differences in the age structures of the Indigenous and non-Indigenous populations (view technical glossary for details of standardisation).

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 [12]; ABS & AIHW, 2005 [7]; Zhao, Condon and Garling, 2004 [11]

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 [7, 13] . 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 a 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 [14] .

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 be greater than suggested by the rate ratios listed in the Table, particularly for Queensland and, to a lesser extent, WA and SA [7] .

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What do we know about the types of cancer occurring among Indigenous people? (November 2007)

The patterns of cancer differ to some extent 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 [7] . 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, and cancer of the uterus.

In terms of specific cancers, the incidence rates were higher for Indigenous people than for non-Indigenous people for:

•  lung cancer
•  intra-oral, pharyngeal and oesophageal cancer
•  pancreatic cancer
•  stomach cancer
•  liver cancer
•  gallbladder cancer
•  cervical cancer
•  unspecified cancers

and lower for Indigenous people than for non-Indigenous people for:

•  skin and lip cancer
•  prostate cancer
•  female breast cancer
•  bowel cancer
•  haematological cancers [15]

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References

1. Cooper S (1992) Elements of human cancer. Boston: Jones and Bartlett Publishers, Inc.
2. American Cancer Society (1992) Cancer facts and figures. Atlanta: American Cancer Society.
3. Australian Cancer Society (2001) Australian Cancer Society Information: facts and figures. Sydney: Australian Cancer Society.
4. Australian Institute of Health and Welfare, Commonwealth Department of Health and Family Services (1998) National health priority areas report: cancer control. Canberra: Australian Institute of Health and Welfare.
5. Australian Institute of Health and Welfare, Australasian Association of Cancer Registries, eds. (2000) Cancer in Australia 1997: incidence and mortality data for 1997 and selected data for 1998 and 1999. Canberra: Australian Institute of Health and Welfare.
6. Tomatis L, ed. (1990) Cancer: causes, occurrence and control. Lyon: International Agency for Research on Cancer.
7. 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
8. 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
9. 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 Australia;180(10):504-511
10. Kirov E, Francis J, Thomson N (2003) Cancer. In: Thomson N, ed. The health of Indigenous Australians . South Melbourne: Oxford University Press:207-223
11. Zhao Y, Condon JR, Garling LS (2004) Cancer incidence and mortality, Northern Territory 1991-2001. Darwin, NT: Department of Health and Community Services
12. 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
13. Condon JR, Zhao Y, Armstrong BK, Barnes A (2004) Northern Territory Cancer Register, data quality 1981-2001. Darwin: Department of Health and Community Services
14. 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
15. Roder D (2007) Epidemiology of cancer in Indigenous Australians: implications for service delivery. Paper presented at the 9th National Rural Health Conference: standing up for rural health: learning from the past, action in the future 7-10 March 2007, Albury, NSW

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Last updated: 8 November 2007