Terminology, molecular features, epidemiology, and management of serrated colorectal neoplasia

In addition to the adenoma-to-carcinoma sequence, colorectal carcinogenesis can occur through the serrated pathway. World Health Organization guidelines assign serrated polyps to hyperplastic polyps, traditional serrated adenomas and sessile serrated lesions, the latter two being precursors of colorectal cancer. The serrated pathway is characterised by mutations in RAS and RAF, disruption of WNT signalling and widespread methylation of CpG islands. The prevalence of serrated-class polyps is 20 to 40% in average-risk individuals, most of them hyperplastic; sessile serrated lesions, the most common premalignant serrated subtype, are found in up to 15% of average-risk patients by high-detecting endoscopists. Variation in endoscopic detection rates points to the need for careful examination with adequate bowel preparation and sufficient withdrawal time. Risk factors for sessile serrated lesions include white race, family history of colorectal cancer, smoking and alcohol intake, and patients with serrated polyps have an increased risk of synchronous and metachronous advanced neoplasia.