The National Bowel Cancer Screening Program (NBCSP) started in Australia in 2006. Its aim is to reduce morbidity and mortality from bowel cancer by actively recruiting and screening the target population for early detection or prevention of the disease. An earlier study (AIHW 2014) quantified and evaluated the effectiveness of the NBCSP for 2006–2008 invitees against this aim. This current report extended those findings by linking a larger NBCSP invitee cohort (2006–2010) to more recent cancer incidence and mortality data to analyse 51,832 people diagnosed with bowel cancer in 2006–2015. Of these:
- 15,454 were invited to participate in the NBCSP in 2006–2010 as part of the target population’s turning 50, 55 or 65 (NBCSP invitees)
- 36,378 were aged 50–74 when diagnosed, but did not turn 50, 55 or 65 in 2006–2010 and were therefore not invited to screen in that period (non-invitees).
This report compares the outcomes (mortality) and cancer characteristics of these two populations. It shows that NBCSP invitees (particularly those who participated) had less risk of dying from bowel cancer, and were more likely to have less-advanced bowel cancers when diagnosed, than non-invitees. These findings confirm that the NBCSP is contributing to reducing morbidity and mortality from bowel cancer in Australia.
Bowel cancer and all-cause mortality rates were lower for NBCSP invitees than non-invitees
Of the people diagnosed with bowel cancer in this study, non-invitees had a 28% higher risk of bowel cancer death by 31 December 2015 compared with NBCSP invitees. Even after correcting for lead-time bias in screen-detected cancers (where an earlier diagnosis may not affect eventual date of death, yet give a seemingly longer survival time), the mortality risk was still a statistically significant 13% higher for non-invitees. The all-cause mortality risk was also found to be a statistically significant 7% higher for non-invitees.
Among NBCSP invitees specifically, the risk of death from bowel cancer was over 2 times as high in those who did not participate but later had a bowel cancer diagnosed, compared with those whose cancer was diagnosed through participation in the NBCSP.
On average, bowel cancers were less advanced for NBCSP invitees than non-invitees
Detection of bowel cancer at an earlier stage in its development is associated with better treatment options and prognosis, and is a key reason behind the reduced mortality risk. Of the bowel cancers in this study with ‘summary stage at first presentation’ data available, non-invitees were found, on average, to have more advanced (worse prognosis) bowel cancers compared with NBCSP invitees. Specifically, bowel cancers in non-invitees had 12% higher odds of being more advanced than those diagnosed in NBCSP invitees.
Among NBCSP invitees, those with screen-detected bowel cancers were much more likely to be diagnosed at an earlier summary stage (171% higher odds), compared with bowel cancers later diagnosed in the invitees who did not participate.
Bowel cancers diagnosed within 2 years of a negative or inconclusive screening test
Compared with screen-detected bowel cancers, those diagnosed within 2 years of a negative or inconclusive screening test were more likely to be in the right side of the bowel, be of a non-adenocarcinoma cell type, and less likely to be localised.
Screening test performance
Of the NBCSP invitees who participated, 85% of those diagnosed with bowel cancer within 2 years of their screen received a positive screening result, and 92% of those who were not diagnosed with bowel cancer received a negative result. These figures suggest that the screening test used at the time of this study had a high degree of accuracy.