Christou et al. BMC Public Health 2010, 10:373 http://www.biomedcentral.com/1471-2458/10/373 1. Descriptive review 1.1 Bowel cancer in Indigenous Australians- epidemiology and data quality Although bowel cancer is rarely noted as a significant health issues for Indigenous Australians, it is the third most common cancer after lung and breast in women, and lung and prostate in men, accounting for about 10% and 9% of all cancers respectively [13]. However, the lack of national data has meant that little information is available surrounding the impact of bowel cancer on Indigenous Australians. The Australian Institute of Health and Welfare (AIHW) reports that incidence and deaths from bowel cancer are much lower than the non-Indigenous population [13], although the true mag- nitude of bowel cancer is not clear due to problems associated with under-ascertainment of Indigenous sta- tus in cancer data collection registries. The Australian Government recognizes three criteria as determining Aboriginal and Torres Strait Islander status: - Indigen- ous descent; self-identification as an Indigenous person and acceptance of the individual as Indigenous by the Indigenous community [14]. Administrative data collec- tions generally focus on self-identification to classify an individual as Indigenous, and while ascertainment of Indigenous status is improving over time in Australia, under ascertainment is an acknowledged problem with gaps in the data that affect the accuracy of statistics recorded [14]. Consequently, Indigenous cancers are thought to be underestimated by up to 20% and mortal- ity up to 35% [13,15,16]. The observed low incidence and mortality from bowel cancer may be influenced by a number of other factors, including the high rate of incomplete or inadequate death certification and the large proportion of cancers of undefined primary site in registered Indigenous can- cer records [13,17]. Additionally, as cancer risk increases with advancing age, the substantially lower life expec- tancy of Indigenous Australians means they may die from other chronic conditions prior to cancer diagnosis [18]. Lower participation in cancer screening and the possibility that Indigenous people with bowel cancer may avoid seeking medical care for symptoms or acces- sing treatment could also reduce ascertainment of dis- ease [19-22]. Age-standardized incidence rates from 2002-2004 sug- gest that the rate of bowel cancer in Indigenous Austra- lians is about half that of the non-Indigenous population (39.7 vs 76.4 per 100 000 in males and 36.6 vs 52.4 in females; rate ratios are 0.5 for males and 0.7 for females) [13]. Incidence data collected from cancer registries (2002-2006) in three Australian states which have the most reliable data collections gave a slightly lower overall age standardized rate of 29.9 per 100 000 among Indigenous people compared to 64.7 per 100 000 Page 3 of 21 in non-Indigenous [16]. However, these figures mask higher rates that exist in younger Indigenous Austra- lians. Age-specific rates show that incidence was similar in non-Indigenous and Indigenous people up until age 50. Notably, men in the 40-49 year age group were found to have higher rates of rectal cancer than non- Indigenous men, attributed to greater consumption of alcohol. Supporting the increased burden at a younger age are findings from the Northern Territory (NT) indi- cating that incidence rate ratios were higher in Indigen- ous Australians under 64 years compared to those over 64 years (0.6 vs 0.2; 1991-2001) [3,4]. Colorectal cancer (CRC) mortality estimates vary in different jurisdictions. In a NT study (1987-95), age standardised mortality rates in Indigenous people were about half that of non-Indigenous people [22], while in rural and remote Queensland and in New South Wales mortality rates were not significantly different between Indigenous and non-Indigenous people [15,23]. A more recent NT analysis showed mortality rates were similar in Indigenous compared to non-Indigenous people under 65 years, but substantially lower in older ages, suggesting an interaction between age and Indigenous status [24]. This was further supported by recent results from four Australian states, where despite somewhat lower age standardised death rates in Indigenous people (17.9 per 100 000 compared to 19.8 in the non-Indigen- ous population) age-specific mortality rates were actually higher in Indigenous people under 60 years compared to the non-Indigenous population [25]. Indigenous Australians generally have higher mortality following a cancer diagnosis compared to non-Indigen- ous Australians, especially for those cancers which are amenable to early diagnosis and treatment [22,26]. Later staging at diagnosis means patients present with more advanced disease and experience poorer treatment out- comes; Indigenous people also appear less likely to undergo and comply with treatment [19,21]. This has also been shown to be true for CRC [21]. Thus, once diagnosed, Indigenous people are more likely to die from CRC compared to their non-Indigenous counter- parts as reflected in the poorer five year survival rate. Condon et al. [21] found that nearly 90% of Indigenous people with CRC in the NT presented with advanced disease at diagnosis as opposed to 68% of the non-Indi- genous group, and that five year survival was only 31% compared to 55% in the non-Indigenous group [4]. This pattern is consistent with CRC mortality and survival observed in Maori, Native Americans, Native Hawaiians, First Nations and Inuit [6,27-31]. Reasons behind late presentation and delayed diagno- sis have been explored in studies examining breast and cervical cancer in Indigenous people and include a low awareness of symptoms, delay in seeking medical advice,