Mortality and Morbidity: Colorectal Cancer

Close to 90% of people diagnosed with colorectal cancer at the earliest stage are alive five years later (if other causes of death are excluded). However, most cases are detected at a later stage.

Cancer is a National Health Priority Area. These areas are highlighted by health ministers for the attention of policy makers and the public as they add significantly to the burden of disease in Australia, but also have the potential for significant health gains. Colorectal cancer is one of eight cancers prioritised within the National Health Priority Framework. It is the most commonly occurring cancer in Australia (excluding non-melanomic skin cancer for which data are not available), and the second most common cancer-related cause of death, responsible for 4,447 deaths in 2003.

Colorectal cancer has features which set it apart from most other cancers. Most cases are thought to originate in benign lesions (adenomas), which can be detected and removed. Once a cancer develops it remains localised for a relatively long period, with a high proportion of people surviving five years after diagnosis if their cancer is detected and treated at this early stage. However, most cases are detected at a later stage and so, overall, close to 60% of people diagnosed with the disease survive five years (if other causes of death are excluded) (endnote 1).

Colorectal cancer is therefore a focus of policy interest because of the possibility that the mortality rate could be reduced through screening programs to detect adenomas and cancers. Further, there have been moves to reduce mortality and improve the quality of life of colorectal cancer patients by encouraging best practice by clinicians. Finally, because some risk factors for this cancer are reasonably well understood, there is potential for preventing the disease.

Data sources and definitions Information in this article on the incidence of colorectal cancer are drawn from data held by the National Cancer Statistics Clearinghouse, at the Australian Institute of Health and Welfare (AIHW). Survival information is reproduced from research by the Cancer Monitoring Unit of the AIHW, based on incidence data and other data. Mortality data are from the ABS Causes of Death collection. Data on diet, weight, exercise habits and smoking were collected in ABS National Health Surveys. Cancer (malignant neoplasm) is a group of diseases consisting of the uncontrolled growth of cells capable of spreading to other parts of the body, replacing normal tissue (Codes C00-C97 of the International Classification of Diseases and Related Health Problems, 10th revision (ICD-10)). Colorectal cancer is cancer that originates in the inner wall of the colon or rectum (Codes C18-C21 of ICD-10). Crude incidence rate of colorectal cancer is the number of new cases reported to Australian cancer registries in a year, per 100,000 population. Age-specific incidence rate of colorectal cancer is the number of new cases affecting people of a specific age group, reported to Australian cancer registries in a year, per 100,000 population in that age group. Age-standardised incidence rate of colorectal cancer is the incidence rate which would have prevailed in a particular year if the population had had the same age structure as the 2001 Australian population. Age-standardising enables comparison of rates between populations with different age structures. Risk of developing colorectal cancer before the age of 75 years approximates the risk of developing colorectal cancer before this age, assuming that the risk remains at 2002 levels throughout life.

NEW CASES

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%.

Mortality and Survival Deaths from colorectal cancer are deaths where the underlying cause of death, listed on the medical certificate of cause of death, is colorectal cancer (Codes C18-C21 of ICD-10). Age-standardised death rate is the death rate which would have prevailed in a particular year if the population had had the same age structure as the 2001 Australian population. In cancer statistics, survival refers to periods of time lived after diagnosis. Five year relative survival proportions represent the proportion of all people diagnosed with colorectal cancer in a particular period who would survive at least five years after diagnosis if other causes of death are excluded. A five year period is widely used in cancer survival measures, although some people who survive five years will subsequently die of the disease. For example, in one Australian study, relative survival proportions for people diagnosed with colorectal cancer were 51% after five years, decreasing to 49% after ten years. (endnote 6) Survival should not be confused with cure, which in cancer statistics generally refers to people who have survived sufficient time after diagnosis that their chance of dying of the disease is estimated to be the same as that of people in the general population who have not been diagnosed with the disease.

MORTALITY

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.




SURVIVAL

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

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).

Survival by stage at diagnosis The stage colorectal cancer has reached before diagnosis is a strong factor affecting likelihood of survival. In Australia and the United States, five year relative survival proportions are around 90% for people whose colorectal cancer is detected while still localised within the bowel wall. (endnote 3) (endnote 4) (endnote 5) As people with such early stage colorectal cancer often have few symptoms, most people are diagnosed at one of the later stages. For example, in a South Australian study, people whose colorectal cancer was diagnosed at the earliest stage had a five year case survival of 88%, but only 15% of the patients in the study were diagnosed at this early stage. VARIATION IN SURVIVING COLORECTAL CANCER FIVE YEARS, BY STAGE OF DISEASE - AN EXAMPLE FROM SOUTH AUSTRALIA(a) % Stage A: cancer has not penetrated all the layers of the wall of the colon or rectum 88 Stage B: cancer has penetrated all the layers of the wall of the colon or rectum 70 Stage C: cancer has penetrated all the layers of the wall and cancer cells are found in nearby lymph nodes 43 Stage D: secondary cancers are found and/or cancer cells are found in distant lymph nodes 7 (a) Based on patients treated in four South Australian teaching hospitals 1980-1995, whose stage was known (2,906 people). The Kaplan-Meier method was used to estimate five year case survival. The Australian Clinico-Pathological Staging System was used. Source: South Australian Cancer Registry (endnote 3).

OPTIMISING TREATMENT

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).

International comparison In the late 1990s Australia ranked fifth for males and second for females in the incidence of colorectal cancer, out of 173 countries for which information was available. Australia's ranking for mortality from colorectal cancer was somewhat lower than for incidence, fifteenth for males and seventeenth for females. Incidence(a) Mortality(b) Male Female Male Female Australia 47.4 35.9 18.7 13.3 Canada 42.2 30.6 16.1 11.7 France 40.8 25.9 18.2 11.8 Germany 45.5 33.1 19.9 15.7 Japan 49.3 26.5 17.3 11.1 New Zealand 53.0 42.2 23.2 18.6 United Kingdom 39.2 26.5 17.5 12.4 United States 44.6 33.1 15.2 11.6 More developed regions 40.0 26.6 17.7 12.3 Less developed regions 10.2 7.7 6.2 4.7 (a) Number of new cases per 100,000 population, age-standardised to the world population. (b) Number of deaths per 100,000 population, age-standardised to the world population. Source: International Agency for Research on Cancer, World Health Organisation (endnote 8)

RISK FACTORS

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).


ENDNOTES

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.

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