The significance of the small adenoma: a longitudinal study of surveillance colonoscopy in an Australian population

Background The international guidelines for surveillance following the finding of a small tubular adenoma vary between no surveillance or colonoscopy at 5 or 10 years, whereas surveillance after an advanced adenoma is 3 years. Optimization of surveillance reduces the risk of colorectal cancer (CRC) with efficient use of colonoscopy resources. We assessed the risks of advanced colorectal neoplasia following a baseline finding of a small adenoma compared with advanced adenoma. 

Patients and methods A retrospective audit was undertaken of patients enrolled in a CRC surveillance program, wherein regular colonoscopies and screening with faecal immunochemical test (FIT) were provided. Patients diagnosed with either small or advanced adenoma followed by at least one surveillance colonoscopy were included. Advanced adenoma included adenomas with features of villous change, size of at least 10 mm, high-grade dysplasia, three or more small tubular adenomas and traditional and sessile serrated adenomas. Subdistribution hazard ratios were calculated for advanced neoplasia (CRC or advanced adenoma). 

Results Overall, 378 patients (62.6±11.2 years, 57.9% male) were included, with 44.2% diagnosed with small adenoma and 55.5% with advanced adenoma at baseline. The crude cumulative incidence of advanced neoplasia at first surveillance was 13.2 and 18.5% after small and advanced adenoma (P=0.16) (at 45.9 and 35.6 months, respectively), which became significant for advanced adenoma after adjustment (subdistribution hazard ratio=2.55, 95% confidence interval=1.49-4.35, P<001). A positive FIT was the only independent predictor of advanced neoplasia after a small adenoma at baseline colonoscopy (odds ratio=5.05, 95% confidence interval=1.27-20.02, P=0.02).

Conclusions The risk of advanced neoplasia following a small adenoma was lower than that following an advanced adenoma, but was strongly predicted by a positive FIT. Reducing frequency of colonoscopy while providing regular FIT might be a more efficient use of resources for this population.