The National Bowel Cancer Screening Program (NBCSP) was introduced in Australia in 2006 with the aim of reducing morbidity and mortality from bowel cancer, by actively recruiting and screening the target population for early detection or prevention of the disease. This study set out to evaluate and to quantify the effectiveness of the NBCSP against this aim.

The study linked NBCSP, cancer incidence and mortality data to identify 22,051 people diagnosed with bowel cancer:

  • 4,327 had been invited to participate in the NBCSP in 2006-2008, as part of the target population turning 50, 55 or 65 (NBCSP invitees)
  • 17,724 were aged 50-69 in 2006-2008, but did not turn 50, 55 or 65 during that period and were therefore not invited to screen then (non-invitees).

The report presents a comparison of the outcomes (mortality) and cancer characteristics for these two populations, and 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 demonstrate that the NBCSP is contributing to reducing morbidity and mortality from bowel cancer in Australia.

Bowel cancer mortality rates were lower for NBCSP invitees than non-invitees

Of people in this study who were diagnosed with bowel cancer in 2006-2008, non-invitees had a 68% higher risk of bowel cancer death by 31 December 2011, 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 15% higher for non-invitees.

Among the 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 bowel cancer screening.

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 linked with better treatment options and prognosis, and is a key reason behind the reduced mortality risk. Of the bowel cancers in this study that had '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 38% higher odds of being more advanced than those diagnosed in NBCSP invitees.

Among the NBCSP invitees, those with screen-detected bowel cancers were much more likely to be diagnosed at an earlier summary stage (121% higher odds), compared with bowel cancers later diagnosed in the invitees who did not participate.

Screening test performance

Of the NBCSP invitees who participated, 83% of those diagnosed with bowel cancer within 2 years of their screen had received a positive screening result, and 93% of those who were not diagnosed with bowel cancer had received a negative result. These figures suggest that the screening test has a high degree of accuracy.