Cancer

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Cancer

Cancer is a disease which affects the body’s cells [1][2]. Cells normally grow and multiply in a controlled manner, but when damage occurs in the genetic blueprint (DNA) of a cell, uncontrolled growth can occur; this is cancer. Cancer cells are benign if they ‘do not spread into surrounding areas, or to different parts of the body’ [1], and are not considered dangerous; however, if these cells ‘spread into surrounding areas, or to different parts of the body [metastasise], they are known as malignant’ [1]. Cancerous cells can arise from almost any cell, so cancer can occur almost anywhere in the body.

The impact of cancer on Indigenous people has attracted 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 [3][4]. Indigenous identification in the registries has been improving [5][6], but, due to poor data quality in several jurisdictions, there are currently no national data on cancer incidence among Indigenous people [7]. For those Indigenous patients who are registered with cancer, there is concern that not all are correctly identified as Indigenous [4]. Provision for the identification of Indigenous people is not yet included on all pathology forms and the extent to which Indigenous cancer patients are identified in hospital inpatient statistics varies across Australia [6]. Second, the fact that cancer has often been reported in terms of the proportions of deaths it causes (19% of Indigenous deaths compared with around 30% of non-Indigenous deaths in Australia in 2010 [8], an apparent ratio of 0.6) rather than by rates has tended to give the erroneous impression that cancer does not have a great impact among Indigenous people. An analysis of rates, rather than comparisons of proportions, reveals that during 2006-2010 the ratio of cancer-related deaths was 1.4 for Indigenous and non-Indigenous people living in NSW, Qld, WA, SA and the NT [7].

Extent of cancer among Indigenous people

Incidence

In the five-year period 2004-2008, an average of 775 Indigenous people living in NSW, Qld, WA and the NT were diagnosed with cancer each year [7].8 After age-adjustment, the cancer incidence rate was 1.1 times higher for Indigenous people than for non-Indigenous people during this period (461 and 434 cases per 100,000 people, respectively).9

The most common cancer diagnosed among Indigenous people living in NSW, Qld, WA and the NT in 2004-2008 was lung cancer (average of 121 cases per year), followed by breast cancer (among Indigenous females) (average of 88 cases per year), and bowel cancer (average of 70 cases per year) [7]. The age-standardised incidence rate for cervical cancer was 2.8 times higher for Indigenous women than for non-Indigenous women (Table 14) [9]. Age-standardised incidence rates for Indigenous people were 1.9 times higher for lung cancer and cancer of the unknown primary site than those for non-Indigenous people, but rates were lower for Indigenous people than for non-Indigenous people for breast cancer, prostate cancer, bowel cancer, non-Hodgkin lymphoma, and melanoma of the skin.

For all types of cancer, the mean age of diagnosis was lower for Indigenous males and females living in NSW, Qld, WA and the NT in 2004-2008 than for their non-Indigenous counterparts [10].

Table 14: Age-standardised incidence rates for selected cancers, by Indigenous status, and Indigenous:non-Indigenous rate ratios, NSW, Qld, WA and the NT, 2004-2008

Site of primary cancer	Indigenous people	Non-Indigenous people	Rate ratio
Source: AIHW and Australasian Association of Cancer Registries, 2012 [9]
Notes: Rates per 100,000 population Ratio is the Indigenous rate divided by the non-Indigenous rate Rates are age-standardised to the Australian population at 20 June 2001 Due to the incomplete identification of Indigenous status, these figures probably under-estimate the true difference between Indigenous and non-Indigenous rates Levels of missing data on Indigenous identification for prostate cancer (16%) and melanoma of the skin (41%) were particularly high
Lung	80	43	1.9
Breast (females)	82	104	0.8
Prostate (males)	105	148	0.7
Bowel	48	59	0.8
Cervix (females)	18	7	2.8
Pancreas	15	10	1.5
Non-Hodgkin lymphoma	14	16	0.9
Skin (melanoma)	9	32	0.3
Unknown primary site	24	12	1.9

Hospitalisation

There were 4,689 cancer-related hospital separations identified as Indigenous in NSW, Vic, Qld, WA, SA and the NT in 2010-11 [11]. Age-standardised hospitalisation rates for cancer were lower for Indigenous people than for non-Indigenous people (16 and 25 per 1,000, respectively) [12].

In terms of specific cancers, the age-standardised hospitalisation rate for lung cancer for Indigenous people living in NSW, Vic, Qld, WA, SA and the NT in 2008-09 was 1.5 times higher than for their non-Indigenous counterparts [13]. The hospitalisation rate for cervical cancer for Indigenous women living in NSW, Vic, Qld, WA, SA and the NT for the period 2005-06 to 2009-10 was 3.1 times higher than that for other females [14].

Mortality

In the five-year period 2006-2010, there was an average of 424 deaths from cancer per year among Indigenous people living in NSW, Qld, WA, SA and the NT, the second most common cause of death in this period [7]. The age-standardised death rate for cancer for Indigenous people (249 per 100,000) was 1.4 times higher than the rate for their non-Indigenous counterparts.

In terms of specific cancers, an annual average of 104 cancer-related deaths among Indigenous people living in NSW, Qld, WA, SA and the NT in 2006-2010 was from lung cancer, 27 from cancer of an unknown primary site, 27 from breast cancer (among women), and 22 from bowel cancer [9]. Death rate ratios were higher for Indigenous people than for their non-Indigenous counterparts for cervical cancer (4.4), lung cancer (1.8), cancer of an unknown primary site (1.7), female breast cancer (1.3), and pancreatic cancer (1.3) (Table 15).

Table 15: Age-standardised death rates for selected cancers, by Indigenous status, and Indigenous:non-Indigenous rate ratios, NSW, Qld, WA, SA and the NT, 2006-2010

Site of primary cancer	Indigenous people	Non-Indigenous people	Rate ratio
Source: AIHW and Australasian Association of Cancer Registries, 2012 [9]
Notes: Rates per 100,000 population Ratio is the Indigenous rate divided by the non-Indigenous rate Rates age-standardised to the Australian population at 20 June 2001 Due to the incomplete identification of Indigenous status, these figures probably under-estimate the true difference between Indigenous and non-Indigenous rates Levels of missing data on Indigenous identification for prostate cancer (16%) and melanoma of the skin (41%) were particularly high
Lung	61	34	1.8
Breast (female)	27	22	1.3
Prostate (males)	30	30	1.0
Bowel	15	17	0.9
Pancreas	13	10	1.3
Cervix (females)	8	2	4.4
Non-Hodgkin lymphoma	5	6	0.9
Skin (melanoma)	2	6	0.4
Unknown primary site	17	10	1.7

The patterns of Indigenous cancer incidence and mortality are largely explained by the higher level of risk factors, most notably tobacco use [15][16][17]. For example, high rates of smoking are the likely cause of a high incidence of cancers of the lung, mouth and throat [18].

The slightly higher Indigenous:non-Indigenous ratio for cancer incidence (1.1) than for deaths from cancer (1.4) could be due to a number of factors [4]:

• Indigenous people are significantly more likely to have cancers that have a poor prognosis
• Indigenous people are usually diagnosed with cancer at a later stage (probably due to a combination of later presentation for health care and lower participation in screening programs)
• Indigenous people are less likely to receive optimal treatment.

References

1. Cancer Council Australia (2012) What is cancer?. Retrieved 2 November 2012 from http://www.cancer.org.au/about-cancer/what-is-cancer/
2. Australian Cancer Research Foundation (2012) What is cancer?. Retrieved 2 November 2012 from http://www.acrf.com.au/on-cancer/
3. 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
4. Cunningham J, Rumbold AR, Zhang X, Condon JR (2008) Incidence, aetiology, and outcomes of cancer in Indigenous peoples in Australia. Lancet Oncology; 9(6): 585-595
5. Zhang X, Condon JR, Rumbold AR, Cunningham J, Roder DM (2011) Estimating cancer incidence in Indigenous Australians. Australian and New Zealand Journal of Public Health; 35(5): 477-485
6. Australian Institute of Health and Welfare (2010) Australia's health 2010: the twelfth biennial report of the Australian Institute of Health and Welfare. Canberra: Australian Institute of Health and Welfare
7. Australian Institute of Health and Welfare, Australasian Association of Cancer Registries (2012) Cancer in Australia: an overview 2012. Canberra: Australian Institute of Health and Welfare
8. Australian Bureau of Statistics (2012) Causes of death, Australia, 2010. Canberra: Australian Bureau of Statistics
9. Australian Institute of Health and Welfare, Australasian Association of Cancer Registries (2012) Cancer in Australia: an overview 2012: supplementary tables. Canberra: Australian Institute of Health and Welfare
10. Australian Health Ministers’ Advisory Council (2012) Aboriginal and Torres Strait Islander health performance framework: 2012 report. Canberra: Office for Aboriginal and Torres Strait Islander Health, Department of Health and Ageing
11. Australian Institute of Health and Welfare (2012) Australian hospital statistics 2010-11. Canberra: Australian Institute of Health and Welfare
12. Australian Institute of Health and Welfare (2012) Australian hospital statistics 2010-11 supplementary tables. Canberra: Australian Institute of Health and Welfare
13. Australian Institute of Health and Welfare, Cancer Australia (2011) Lung cancer in Australia: an overview. Canberra: Australian Institute of Health and Welfare
14. Australian Institute of Health and Welfare (2012) Gynaecological cancers in Australia: an overview. Canberra: Australian Institute of Health and Welfare
15. Threlfall TJ, Thompson JR (2009) Cancer incidence and mortality in Western Australia, 2007. Perth: Department of Health, Western Australia
16. 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
17. Condon J (2004) Cancer, health services and Indigenous Australians. Canberra: Office for Aboriginal and Torres Strait Islander Health, Cooperative Research Centre for Aboriginal and Tropical Health
18. Australian Bureau of Statistics, Australian Institute of Health and Welfare (2008) The health and welfare of Australia's Aboriginal and Torres Strait Islander Peoples 2008. Canberra: Australian Bureau of Statistics and Australian Institute of Health and Welfare

Endnote

8. The overall level of missing data on Indigenous status for cancers diagnosed between 2004 and 2008 in NSW, Qld, WA and the NT was 12%.

9. Cancer incidence rates have been reported previously as lower for Indigenous people than for non-Indigenous people. The current report notes that the changed relativity could be due to differences in the jurisdictions contributing to the various reports, but it may also reflect real changes in the incidence of cancer among Indigenous people.