The occurrence and detection of metachronous colorectal tumors are important for determining appropriate intervals of surveillance colonoscopy for polyps. Clinically significant serrated polyps (CSSPs) include sessile serrated lesions (SSLs), traditional serrated adenomas, hyperplastic polyps (HPs) ≥10 mm, and proximal HPs of 5–9 mm. CSSPs are associated with the metachronous large, serrated polyps, which are at risk for colorectal cancer. Meanwhile, HPs are subclassified in the WHO classification into microvesicular HPs (MVHPs) and goblet cell-rich HPs (GCHPs). MVHPs and GCHPs differ in molecular biological behavior, histology, and endoscopic findings, and MVHPs have been shown to resemble SSLs. To date, no studies have compared the metachronous tumors of SSLs, MVHPs, and GCHPs among CSSPs; thus, we investigated the metachronous polyps.

This study was a single-center cohort study conducted at Toyoshima Endoscopy Clinic. We obtained data from the Toyoshima Endoscopy Clinic Database. This study was approved by the institutional review board of the Yoyogi Mental Clinic (approval no. RKK227). We evaluated patients who underwent their first (index) and second (surveillance) colonoscopy at the Toyoshima Endoscopy Clinic between April 2017 and August 2024. HPs that met the CSSP criteria (i.e., ≥ 10 mm or ≥ 5 mm at proximal colon) were enrolled in this study. We assessed the effect of detection rates of SSLs, MVHPs, and GCHPs at index colonoscopy on the time to detections of metachronous SSLs, MVHPs, GCHPs, and adenomas. Hazard ratios (HRs) were calculated to adjust for age and sex using Cox proportional hazards models.

A total of 3174 patients (male sex, 43.6%; mean age, 51.2 years; median surveillance period, 499 days) were enrolled. A family history of colorectal cancer was present in 7.56% of patients. Detection rates of SSLs, MVHPs, GCHPs, and conventional adenomas were 7.69%, 5.36%, 0.54%, and 56.76%, respectively. The detection rate of SSLs at index colonoscopy was associated with the detection of metachronous SSLs (HR 6.19, odds ratio [OR] 4.51-8.50, P < 0.001), MVHPs (HR 6.83, OR 4.74-9.85, P < 0.001), GCHPs (HR 4.25, OR 1.73-10.46, P = 0.002), and conventional adenomas (HR 1.38, OR 1.11-1.70, P = 0.003). The detection rate of MVHPs at index colonoscopy was associated with metachronous SSLs (HR 5.13, OR 3.54-7.43, P < 0.001), MVHPs (HR 4.56, OR 2.92-7.12, P < 0.001), and conventional adenomas (HR 1.38, OR 1.10-1.75, P = 0.006). The detection rate of GCHPs at index colonoscopy was associated with the detection of metachronous GCHPs (HR 19.01, OR 4.45-81.18, P < 0.001).

This cohort study investigated metachronous polyp detection in patients with CSSPs. Detection rates of index SSLs and MVHPs were associated with metachronous detection of both SSLs and MVHPs. Detection of index GCHPs was associated with metachronous detection of GCHPs. MVHPs and GCHPs were mutually exclusive in metachronous detection