Synthetic indicator of the impact of colorectal cancer screening programmes on incidence rates

The impact of a screening programme on colorectal cancer (CRC) incidence in its target population depends on several variables, including coverage with invitations, participation rate, positivity rate of the screening test, compliance with an invitation to second-level assessment and endoscopists' sensitivity. We propose a synthetic indicator that may account for all the variables influencing the potential impact of a screening programme on CRC incidence.We defined the 'rate of advanced adenoma on the target population' (AA-TAP) as the rate of patients who received a diagnosis of advanced adenoma within a screening programme, divided by the programme target population. We computed the AA-TAP for the CRC Italian screening programmes (biennial faecal immunochemical test, target population 50-69 year olds) using the data of the Italian National Survey from 2003 to 2016, overall and by region, and assessed the association between AA-TAP and CRC incidence fitting a linear regression between the trend of regional CRC incidence rates in 50-74 year old subjects and the cumulative AA-TAP.In 2016, the AA-TAP at a national level was 105×100 000, whereas significant differences were observed between the northern and central regions (respectively 126 and 149×100 000) and the South and Islands (36×100 000). The cumulative AA-TAP from 2004 to 2012 was significantly correlated with the difference between CRC incidence rates in 2013-2014 and those in 2003-2004 (p=0.009).The AA-TAP summarises into a single indicator the potential impact of a screening programme in reducing CRC incidence rates.