Mid-term effects of faecal immunochemical test screening on colorectal cancer incidence by tumour site

The supposedly lower sensitivity of the faecal immunochemical test (FIT) for proximal colon tumours is an open question. We compared the observed annual (1997-2017) tumour site-specific incidence rates of colorectal cancer (CRC) in the target population (over 1,300,000 aged 50-69 years) of an Italian regional FIT screening programme with the rates that would be expected in the absence of screening.

For proximal colon cancer, the expected rates were estimated with an age-period model in both sexes combined, showing an increasing trend. For distal colon cancer and rectal cancer, the best fit to the observed rates was provided by an age-period-cohort model (men) and an age-period model (women), both showing a stable trend.

In the 11th and 12th full years of screening, the decrease in incidence was of the same magnitude for proximal colon cancer (rate ratio: 0.55 and 0.49 among men; 0.63 and 0.57 among women) and distal colon cancer (0.50 and 0.50; 0.60 and 0.61). The decrease was less pronounced for rectal cancer.

Thanks to the increase in the modelled expected incidence of proximal colon cancer alone, the impact of FIT screening on the incidence of CRC was similar between colonic segments.