Five year colorectal cancer outcomes in a large negative CT colonography screening cohort.

OBJECTIVES: To assess the 5-year incidence of clinically presenting colorectal cancers following a negative CT colonography (CTC) screening examination, as few patient outcome data regarding a negative CTC screening result exist.
METHODS: Negative CTC screening patients (n = 1,050) in the University of Wisconsin Health system over a 14-month period were included. An electronic medical record (EMR) review was undertaken, encompassing provider, colonoscopy, imaging and histopathology reports. Incident colorectal cancers and other important GI tumours were recorded.
RESULTS: Of the 1,050 cohort (mean [±SD] age 56.9 ± 7.4 years), 39 (3.7%) patients were excluded owing to lack of follow-up within our system beyond the initial screening CTC. The remaining 1,011 patients were followed for an average of 4.73 ± 1.15 years. One incident colorectal adenocarcinoma represented a crude cancer incidence of 0.2 cancers per 1,000 patient years. EMR revealed 14 additional patients with clinically important GI tumours including: advanced adenomas (n = 11), appendiceal goblet cell carcinoid (n = 1), appendiceal mucinous adenoma (n = 1) and metastatic ileocolonic carcinoid (n = 1). All positive patients including the incident carcinoma are alive at the time of review.
CONCLUSIONS: Clinically presenting colorectal adenocarcinoma is rare in the 5 years following negative screening CTC, suggesting that current strategies, including non-reporting of diminutive lesions, are appropriate. KEY POINTS: • CT colonography (CTC) screening is increasingly used to identify potential colorectal cancer. • Clinically presenting cancers are rare for 5 years following negative CTC screening. • The practice of setting a 6 mm polyp size threshold seems safe. • An interval of 5 years for routine CTC screening is appropriate.