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COMPLEXITIES IN THE MEASUREMENT OF BOWEL CANCER IN AUSTRALIA
WHAT IS THE ISSUE?
The bowel is the section of the gastrointestinal tract which comes after the stomach. It is made up of the small bowel (or small intestine) and the large bowel (large intestine). In the International Classification of Diseases (ICD), cancer sites specified within the bowel include the small intestine, the colon, the rectosigmoid junction, the rectum, anus and anal canal.
When classifying causes of death, the ABS uses an internationally agreed common rule set determined by the World Health Organization (WHO). This rule set states that cancers of the digestive tract must be coded to a specified site within the digestive system. Where the site is not specified in sufficient detail on the death certificate, the rules state that the cancer should be coded to a less specified code - in this case C26.0 Malignant neoplasm of the intestinal tract, part unspecified. As the term 'bowel cancer' does not specify the location of the cancer within the bowel, deaths certified using this term are coded to C26.0.
In Australia the term 'bowel cancer' is commonly used by doctors when actually referring to cancer of the colon or rectum (Bowel Cancer Australia). Deaths certified with this term are coded to C26.0 in line with the internationally agreed rule set, and are not included with the cancers of specified sites including C18-C21 Colon, sigmoid, rectum and anus cancer. As this is the group used by the ABS when reporting on leading causes, any deaths thought of by certifying doctors as colon or rectum cancers but described with the more general term 'bowel cancer' will not be included in this leading cause grouping.
Work undertaken by Australian cancer registries has found that almost all deaths certified as bowel cancer are actually cancers of the colon, sigmoid or rectum. This is important as it indicates that most (if not all) deaths certified as bowel cancer and currently coded to C26.0 could have been included in the C18-C21 leading cause grouping.
HOW IS THE DATA AFFECTED?
The leading cause grouping Colon, sigmoid, rectum and anus cancers (C18-C21) presented in this publication accounted for 4,433 deaths. This made it the seventh leading cause of death in 2015, and the second leading cause of cancer deaths. Malignant neoplasms of the intestinal tract, unspecified (C26.0), accounted for 1,110 deaths in 2015. If these deaths were included in the existing colon cancer grouping, this would result in a total of 5,543 deaths, and would make it the sixth leading cause of death in 2015 (overtaking diabetes). Although the ranking of colon cancer in the overall leading causes of death would change, it would remain the second leading cause of cancer deaths, with lung cancer remaining as the leading cause of cancer mortality.
Colon cancer (C18-C21) and Malignant neoplasms of the intestinal tract, part unspecified (C26.0), 2015(a)
Footnote(s): (a) All causes of death data from 2006 onward are subject to a revisions process - once data for a reference year are 'final', they are no longer revised. Affected data in this table are: 2006-2012 (final), 2013 (revised), 2014-2015 (preliminary). See Explanatory Notes 52-55 and A More Timely Annual Collection: Changes to ABS Processes (Technical Note) in this publication. See also Causes of Death Revisions, 2012 and 2013 (Technical Note) in Causes of Death, Australia, 2014 (cat. no. 3303.0).
The classification of deaths certified as 'bowel cancer' to C26.0 evidently leads to an underestimate of deaths due to colon cancer. The ABS will continue to work with the WHO to recommend improvements to the international classification and coding system to maximise its fit in the Australian context, including for bowel cancer.
However, until internationally agreed changes are made and implemented the ABS recommends the following: When making any interpretation or assessment of colon cancer deaths in Australia, consider the high likelihood that many deaths coded to C26.0 Malignant neoplasms of the intestinal tract, unspecified are deaths from colon, sigmoid, rectum and anus cancers.
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