Mixed lesions in premalignant colorectal polyps

Colonoscopists occasionally encounter mixed lesions with overlapping histological features. The frequency and combinations of such mixed colorectal polyps remain poorly understood. We comprehensively analyzed the frequencies and combinations of histologically mixed premalignant colorectal polyps. This study had a retrospective, single-center, cross-sectional design. Patients who underwent colonoscopy at the Toyoshima Endoscopy Clinic between March 2022 and July 2023 were eligible. We excised lesions diagnosed as conventional adenomas or clinically significant serrated polyps. Among these polyps, we focused on mixed lesions and analyzed their frequency and combinations. Among 9,682 resected colorectal lesions, 61 (0.63%) were classified as mixed lesions. The most common combination was microvesicular hyperplastic polyp (MVHP) + goblet cell-rich hyperplastic polyp (GCHP) (41.0%), followed by sessile serrated lesion (SSL) + traditional serrated adenoma (TSA) (21.3%), MVHP + conventional adenoma (9.8%), and TSA + conventional adenoma (9.8%). The mixed rates for MVHPs, GCHPs, SSLs, TSAs, and conventional adenomas were 2.3%, 3.7%, 2.9%, 53.5%, and 0.28%, respectively. Mixed MVHP + GCHP lesions were significantly larger than pure GCHPs (5.3 ‍mm vs 4.0 ‍mm, p<0.01). The frequencies and combinations of mixed premalignant colorectal lesions found in this study may reflect the histogenesis of neoplasia and genetic mutations.