Background: The aim was to identify the patients with colorectal symptoms most likely to benefit from whole colonic imaging (WCI) to diagnose colorectal cancer and those for whom flexible sigmoidoscopy (FS) may be initially sufficient.
Methods: This prospective observational study (16 years) included 16 433 newly referred patients with symptoms or signs of colorectal cancer.
Results: Colorectal cancer was diagnosed in 946 patients (diagnostic yield 5.8 per cent), 815 (86.2 per cent) in the rectum or sigmoid (distal) and 131 (13.8 per cent) in the proximal colon. Some 15 829 patients (96.3 per cent) presented with symptoms alone (without iron deficiency anaemia or abdominal mass). Of 787 cancers in these patients, 750 (95.3 per cent) were distal. The prevalence of proximal cancer above and below the age of 60 years was 0.4 per cent (33 of 8249) and 0.1 per cent (four of 7580) respectively. Of 16 256 patients having FS, 5665 (34.8 per cent) had WCI. Of the other 10 591, five subsequently presented with proximal cancers. FS missed ten (1.3 per cent) of 796 cancers.
Conclusion: Patients with iron deficiency anaemia or a mass require WCI. However, in patients with symptoms alone, FS detects 95 per cent of cancers, and the diagnostic yield of WCI after FS is very low. Alternative management strategies need to be developed to avoid unnecessary investigations in this low-risk group.