Comparison of screen-detected and interval colorectal cancers in the Bowel Cancer Screening Programme

BACKGROUND: The NHS Bowel Cancer Screening Programme (BCSP) offers biennial faecal occult blood testing (FOBt) followed by colonoscopy after positive results. Colorectal cancers (CRCs) registered with the Northern Colorectal Cancer Audit Group database were cross-referenced with the BCSP database to analyse their screening history. METHODS: The CRCs in the screening population between April 2007 and March 2010 were identified and classified into four groups: control (diagnosed before first screening invite), screen-detected, interval (diagnosed between screening rounds after a negative FOBt), and non-uptake (declined screening). Patient demographics, tumour characteristics and survival were compared between groups. RESULTS: In all, 511 out of 1336 (38.2%) CRCs were controls; 825 (61.8%) were in individuals invited for screening of which 322 (39.0%) were screen detected, 311 (37.7%) were in the non-uptake group, and 192 (23.3%) were interval cancers. Compared with the control and interval cancer group, the screen-detected group had a higher proportion of men (P=0.002, P=0.003 respectively), left colon tumours (P=0.007, P=0.003), and superior survival (both P<0.001). There was no difference in demographics, tumour location/stage, or survival between control and interval groups. CONCLUSION: The FOBt is better at detecting cancers in the left colon and in men. The significant numbers of interval cancers weren’t found to have an improved outcome compared with the non-screened population.