Objective Although guaiac-based faecal occult blood test screening has been shown to be effective in reducing colorectal cancer (CRC) mortality, it has been criticised mostly for its low sensitivity. Italian CRC screening programmes are based on immunochemical tests (iFOBT). We collected and analysed the interval cancers (ICs) found by five screening programmes to estimate their sensitivity.

Methods ICs were identified in subjects who had a negative result in a screening examination from 2002 to 2007 (N=267 789); data were linked with 2002–2008 hospital discharge records. Analysis was based on the follow up of 468 306 person-years. The proportional incidence-based sensitivity was estimated overall and by sex, age class, time since last negative iFOBT result, anatomical site, and history of screening (first or subsequent test).

Results Overall, 126 ICs were identified, compared to 572 expected cancers. The proportional incidences were 15.3% and 31.0% in the first and the second interval-years, respectively, with an overall episode sensitivity of 78.0% (95% CI: 73.8 to 81.6). Sensitivity was higher for males than females (80.1% vs 74.8%); no differences were observed by age, anatomical site or between programmes. The test sensitivity of iFOBT was 82.1% (95% CI 78.1% to 85.3%).

Conclusions iFOBT-based screening programmes showed a high performance in terms of sensitivity as estimated through the IC rates. The screening schedule utilised in our programmes (single iFOBT, positivity threshold of 100 ng Hb/ml of sample solution, inter-screening interval of 2 years) shows low rates of missed cancers that are diagnosed during the interval. HDR are a convenient and reliable source of data for IC studies.