National bowel cancer screening program monitoring report: phase 2, July 2008 - June 2011
This report presents statistics on the National Bowel Cancer Screening Program for Australians invited to take part between July 2008 and June 2011. Just over 800,000 people were screened in that time, with about 60,000 found to require further assessment. One out of every 11 colonoscopies performed for further assessment detected and removed an advanced adenoma (pre-cancerous lesion), and a cancer was detected in 1 out of every 33 colonoscopies. However, this represents only a partial picture of outcomes due to incomplete reporting.
The National Bowel Cancer Screening Program (NBCSP) aims to reduce the incidence, illness and mortality related to bowel cancer in Australia through screening to detect cancers and pre-cancerous lesions in their early stages, when treatment will be most successful.
Phase 2 of the NBCSP ran from 1 July 2008 to 30 June 2011 and invited people turning 50, 55 or 65 between 1 January 2008 and 31 December 2010 to screen for bowel cancer. This report focuses on measures of Program performance for these people.
During Phase 2, the Program was suspended for about six months after the screening test was found to be returning a higher rate of negative results than expected. Remediation actions to retest those who may have been affected were undertaken and the apparent effects are also presented in this report.
How many people participated in Phase 2 of the NBCSP?
About 38% of the 2.1 million people invited in Phase 2 returned a completed bowel cancer screening kit for analysis. This overall participation rate was slightly lower than Phase 1, due to the inclusion of 50 year olds in Phase 2, as participation for the other two ages increased in Phase 2 (Table 1).
How many positive screening results were returned in Phase 2?
About 62,000 participants (7.8%) who returned a valid screening test had a positive screening result. These people were encouraged to follow up this result by visiting their primary health care practitioner and having further investigative testing (colonoscopy).
About 71% of those with a positive screening result were recorded as having had a colonoscopy.
How many bowel cancers and adenomas were detected in Phase 2?
One in 33 colonoscopies performed to follow up a positive screening result diagnosed a confirmed (253) or suspected (868) cancer, while advanced adenomas were found in a further 3,333 participants (1 in 11 colonoscopies) investigated. Adenomas are benign growths that have the potential to become cancerous, and their removal is likely to lower the risk of future bowel cancers in these patients.
From the available NBCSP data, almost 80% of bowel cancers removed (resected) were in the earliest two (out of four) stages of cancer spread.
Were there differences between subgroups participating in the NBCSP?
Women were more likely to screen than men; conversely, men had higher rates of screen-detected bowel cancers and overall bowel cancer incidence and mortality.
Aboriginal and Torres Strait Islander participants, participants who spoke a language other than English at home, and participants who lived in Inner regional and Outer regional or areas of lower socioeconomic status had higher rates of positive screening results, yet lower rates of follow-up colonoscopies than other participants.