Serrated polyp (SPs) are precursors to 20%-30% cases of colorectal tumors, but patients' long-term risk after removal of SPs is poorly understood. We investigated the risk of colorectal cancer (CRC) in individuals with a history of SPs.

We performed a retrospective cohort study of Kaiser Permanente Northern California members who underwent colonoscopy from 2006 through 2016. Study participants were categorized based on the size and location of SPs. We used Cox proportional hazards modeling to estimate the hazard ratio (HR) and 95% CI for the association of CRC diagnosed more than 1 y after colonoscopy, with polyp type vs no polyp after adjustment for year of colonoscopy, age, sex, race/ethnicity, and smoking history.

The study included 233,393 individuals, of whom 445 developed incident CRC. At 10 y, the cumulative incidence rates of CRC for individuals with no polyp, proximal small SPs, proximal large SPs, and distal SPs were 4.7 (95% CI, 4.0-5.6), 14.8 (95% CI, 9.0-24.3), 30.2 (95% CI, 13.2-68.4), and 5.9 (95% CI, 3.6-9.5) per 1000 persons, respectively. In patients with SPs, risk of CRC was not increased until 3 y or more after the first colonoscopy (HR for small proximal SPs, 2.6; 95% CI, 1.7-3.9 and HR for large proximal SPs, 8.0, 95% CI, 3.6-16.1). The presence of synchronous adenomas increased the risk for CRC (HR for proximal SPs with synchronous adenomas, 4.0, 95% CI, 3.0-5.5 and HR distal SPs with synchronous adenomas 2.4, 95% CI, 1.7-3.4).

In a retrospective analysis of a large cohort of individuals examined by colonoscopy, we found that risk of incident CRC increases in individuals with proximal SPs (large SPs in particular) 3 y or more after the colonoscopy. These findings support guidelines that recommend surveillance colonoscopy for individuals with SPs.