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.