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Mortality and Morbidity: Colorectal Cancer
Colorectal cancer incidence rates(a)
There were 12,844 new cases of colorectal cancer in 2001, up from 7,093 in 1983. The crude incidence rate of colorectal cancer increased from 46 new cases per 100,000 people in 1983 to 66 new cases per 100,000 in 2001, an increase of 43% (on average, the rate increased by 2% per year). Colorectal cancer is strongly age-related and a large part of this increase in the crude rate was due to the ageing of the population. That is, the age profile of the Australian population changed over the period, so that a larger proportion of the population fell in the older age range, where colorectal cancer is more common.
However, not all of the increase in the incidence of colorectal cancer was due to the ageing of the population. When adjusted to remove the effect of an ageing population, there was an increase of 15% in the incidence rate between 1983 and 2001. This increase stems mostly from increases in incidence that occurred among people aged 55 years and over, while incidence decreased slightly among people aged 40-54 years. Improved detection, due to medical advances or to better public awareness, could account for some of these increases in age-specific incidence rates of colorectal cancer among older people. Such effects have been observed for prostate and cervical cancer (see Australian Social Trends 2004, Cancer Trends).
In 2001, the risk of developing colorectal cancer before the age of 75 years was 1 in 17 for males and 1 in 26 for females.2 At younger ages, colorectal cancer is rare, and about equally as common in males and females. Incidence rises sharply and progressively from the middle years, and rates for men exceed rates for women across the older age groups. This difference was further accentuated between 1983 and 2001 because there was a greater rate of increase in the age-specific incidence rates for older men than for older women. In 1983, the age-standardised incidence rate of colorectal cancer for males was 35% higher than the equivalent rate for females and in 2001 this difference had increased to 43%.
Age-specific incidence rates(a), colorectal cancer
In 2003, 4,447 people died from colorectal cancer: 2,419 males and 2,028 females. After adjusting for the ageing of the population, the death rate from colorectal cancer decreased between 1983 and 2003. The age-standardised death rate was 32.0 deaths per 100,000 population in 1983 and slowly declined to 21.7 deaths per 100,000 in 2002. This downward trend contrasts with the increase in the age-standardised incidence rate between 1983 and 2001. These differing trends in incidence rates and death rates are consistent with increased survival.
Death rate(a), colorectal cancer
More than half of people diagnosed with colorectal cancer are likely to be alive five years after diagnosis. The relative five year survival proportion from colorectal cancer has increased over the last two decades, for both sexes. For males diagnosed over the period 1982-1986 it was 50% but for those diagnosed 1992-1997 it was 58%. For females the increase in relative five year survival proportions was from 52% in 1982-1986 to 59% in 1992-1997. (endnote 1)
Factors which could have impacted on survival data include improved surgical outcomes, an increase in early detection or in detection itself, and the use of adjuvent chemotherapy for stage C and some stage B cancers. Such changes can influence statistics in a number of ways. For example, a trend to earlier diagnosis can of itself add to the average time between diagnosis and death of those who ultimately die from the disease, as well as having an effect through enabling life extending or life saving treatment for others. Improved detection can mean that some cancers are diagnosed in elderly people that previously would have gone undiagnosed.
Screening programs for colorectal cancer, aimed at people at average risk, could potentially save lives. However, this outcome depends on having a screening method that is sufficiently accurate, cost effective and which people are prepared to undergo. In 2002, the Australian Government commenced a pilot screening program aimed at people aged 55-74 years, based on testing stool samples for blood (endnote 6), and in the 2005-06 Budget allocated funds over three years to phase in a national bowel cancer screening program. Some trials suggest that colorectal cancer mortality might be reduced by 15-30% through such a program (endnote 1).
Crude five-year relative survival proportions(a) for colorectal cancer
One part of an Australian colorectal cancer control strategy has been the development of a set of guidelines for the prevention, diagnosis and treatment of colorectal cancer, produced in consultation with experts and professional bodies (endnote 7). The guidelines aim to consolidate advances in knowledge across the medical profession, and inform patients. In 2000, the guidelines were used as a basis for a national survey of clinicians (endnote 9). Feedback was provided to clinicians on how their practice compared with the guidelines. The survey report also contributed to the discussion of cancer control, by examining general issues regarding delivery of care (endnote 9).
Besides age, genetics and behaviour affect a person's risk of developing colorectal cancer. Around one quarter of people diagnosed with colorectal cancer either have an identifiable genetic syndrome which carries a risk of colorectal cancer, or, more commonly, have a first degree relative (i.e. mother, father, sister, brother) who has had the disease (endnote 4). The level of risk of people with a family history of colorectal cancer depends on the combination of relatives who had the disease, at what age, and whether a genetic condition is identified (endnote 7). The NHMRC recommends screening using colonoscopies for people at moderately increased risk or potentially high risk due to their family history (endnote 7). These people make up about 2% of the population (endnote 7).
Around three quarters of people who develop colorectal cancer do not have genetic or medical risk factors (endnote 1). The world wide pattern of incidence of colorectal cancer has led to a focus on behavioural risk factors, particularly diet. Colorectal cancer is more common among people in more developed regions of the world, whose diets differ in a number of respects from those of people in other regions. Although the epidemiological pattern is strong, other types of research investigating specific links between diet and colorectal cancer have had mixed findings (endnote 10).
In Australia, the National Health and Medical Research Council (NHMRC) recommend that a healthy adult diet should include plenty of vegetables, legumes, fruit and cereals (preferably wholegrain), and also lean meat or its alternatives, milk and dairy foods or their alternatives, and only a moderate amount of fat and alcohol. The NHMRC guidelines in respect of vegetables and cereal include protection against colorectal cancer as part of their scientific rationale (endnote 11).
Information on diet and some other behaviour that can affect health were collected in the 2001 ABS National Health Survey. In 2001, about 30% of the population reported that they usually ate four or more serves of vegetables a day (putting them close to the intake recommended by the NHMRC) while 53% met the NHMRC recommendation of at least two serves of fruit per day. Among those who did not meet this intake were 23% of the population who averaged 1 serve or less of vegetables per day and 6% of the population who said they never ate fruit.
A sedentary lifestyle, overweight and obesity, smoking and high levels of alcohol consumption are also suspected risk factors for colorectal cancer (endnote 7) (endnote 12). The Cancer Council of Australia endorses the NHMRC healthy eating guidelines as a broad approach to protecting against cancers in general. It also advocates that people do not smoke, that they avoid or limit alcohol intake, and that they exercise and maintain a healthy weight (endnote 12). Information on these health risk factors was collected in the 1989-90 and 2001 National Health Surveys.
In 2001, close to one third (32%) of people in Australia reported that they were physically inactive in their leisure time (i.e., they did not undertake deliberate exercise, or did so at a very low level, during the survey reference period). Although this was a decrease from 38% in 1989-90, the decrease related mainly to an increase in the proportion who exercised at a low level, rather than to any great increase in the proportion who exercised at a moderate or high level, considered to be more beneficial. This may be partly why 46% of the population were overweight or obese in 2001, up from 38% in 1989-90 (as assessed by Body Mass Index calculated from self-reported height and weight information). (All data are age standardised).
In 2001, 24% of the population were current smokers, down from 28% in 1989-90, mainly due to people quitting smoking. There was little change in respect of risky alcohol consumption: people who consumed alcohol at risky or high risk levels made up about 11% of the population in both 1989-90 and 2001 (for more information see Australian Social Trends 2003 Health risk factors).
1 Australian Institute of Health and Welfare (AIHW) and the Australasian Association of Cancer Registries (AACR) 2003, Cancer in Australia 2000 AIHW Cat. No. CAN 18. AIHW, Canberra (Cancer series no. 23).
2 Australian Institute of Health and Welfare (AIHW) and the Australasian Association of Cancer Registries (AACR) 2004, Cancer in Australia 2001 AIHW Cat. No. CAN 23. AIHW, Canberra (Cancer series no. 28).
3 South Australian Cancer Registry 1997, Epidemiology of Cancer in South Australia. Incidence, Mortality and Survival 1977 to 1996. Incidence and Mortality, 1996. Openbook Publishers, Adelaide.
4 McLeish J A, Thursfield V J and G G Giles 2002, 'Survival from colorectal cancer in Victoria: 10-year follow up from the 1987 management survey' ANZ Journal of Surgery vol. 72 (5) pp. 352-354
5 Ries LAG et al (eds) SEER Cancer Statistics Review 1975-2001, Bethesda Md: National Cancer Institute. <http://seer.cancer.gov/csr /1975–2001/, 2004>accessed 16 Nov 2004.
6 Australian Government. Department of Health and Ageing, Bowel cancer pilot screening program <http://www.cancerscreening.gov.au/> accessed 15 October 2004.
7 National Health and Medical Research Council (NHMRC) 1999, Guidelines for the prevention, early detection and management of colorectal cancer. NHMRC, Canberra.
8 Ferlay J et al (2004) GLOBOCAN 2002: Cancer incidence, mortality and prevalence worldwide IARC Cancer Base No. 5 version 2.0, IARCPress, Lyon, <http://www-dep.iarc.fr/> accessed 29 Mar 2005.
9 Clinical Governance Unit 2002, The National Colorectal Cancer Care Survey; Australian clinical practice in 2000. National Cancer Control Initiative, Melbourne.
10 The American Institute for Cancer Research and the World Cancer Research Fund (1997) Food, nutrition and the prevention of cancer: a global perspective. World Cancer Fund, London.
11 National Health and Medical Research Council 2003, Dietary Guidelines for Australian Adults. Ausinfo, Canberra.
12 The Cancer Council of Australia 2004, National Cancer Prevention Policy 2004-06. The Cancer Council Australia, Sydney.