Interval Cancer in Population-Based Colorectal Screening Programmes: Incidence and Characteristics of Tumours

Simple Summary Faecal occult blood test interval cancer is one of the potential harms of colorectal cancer screening programmes. These tumours are diagnosed in people who have previously received a negative result in a screening test. The objective of this study was to evaluate interval cancer rates in colorectal cancer screening programmes in Spain, assess their risk factors and compare the characteristics of screen-detected and interval cancer tumours. Identifying interval cancer rates as well as the associated factors would make it possible to improve screening strategies and identify personal variables related to the occurrence of interval cancer. Furthermore, studying the characteristics that distinguish interval cancers from screen-detected cancers would help us understand the nature of these tumours. These results would help evaluate and improve colorectal cancer screening programmes, increase their quality and minimise interval cancer in such programmes.Abstract The objective of this study is to evaluate interval cancer (IC) in colorectal cancer (CRC) screening, which is CRC diagnosed in an individual after having received a negative faecal occult blood test and before the next invitation to participate in screening. A follow-up study was conducted on a cohort of participants in the first three screening rounds of four colorectal cancer screening programmes in Spain, n = 664,993. A total of 321 ICs and 2120 screen-detected cancers (SCs) were found. The IC and SC rates were calculated for each guaiac (gFOBT) or immunochemical (FIT) test. A Cox regression model was used to estimate the hazard ratios (HR) of IC risk factors. A nested case-control study was carried out to compare IC and SC tumour characteristics. The IC rate was 1.16 parts per thousand with the gFOBT and 0.35 parts per thousand with the FIT. Men and people aged 60-69 showed an increased probability of IC (HR = 1.81 and HR = 1.95, respectively). There was a decreased probability of IC in individuals who regularly participated in screening, HR = 0.62 (0.47-0.82). IC risk gradually rose as the amount of Hb detected in the FIT increased. IC tumours were in more advanced stages and of a larger size than SC tumours, and they were mostly located in the cecum. These results may play a key role in future strategies for screening programmes, reducing IC incidence.