Two phenotypes of traditional serrated adenomas nationwide survey in Iceland

Iceland has a total population of 300,000 inhabitants. All patients consulting for symptoms of the lower digestive tract during a four-year period (2003-2006) were subjected to a colonoscopic examination; all polyps were endoscopically removed. Out of the total 3,037 colorectal adenomas (CRAs), 308 (10.2%) were traditional serrated adenomas (TSAs). TSAs were divided according the predominant histological phenotype (>50%) into those with ectopic crypt formations (ECF), and those with unlocked serrations (US). ECF-TSA accounted for 5.9% (178/3037) and US-TSA for 4.3% (130/3037). The majority of patients with ECF-TSA and US- TSA were ≥60 years of age (74.1% and 76.2%, respectively). Notwithstanding, when patients having advanced adenomas (with high-grade dysplasia, with or without intramucosal carcinoma) were listed by age, those with ECF-TSA were significantly younger than those with US-TSA (p<0.05). ECF-TSA were more frequently left-sided (71.8%), whereas US-TSA were more frequently right-sided (60.0%). Invasive carcinoma evolved more frequently in ECF-TSA (7.8%) and in US-TSA (7.7%) than in tubular adenomas and in villous/tubulovillous adenonas (0.1% and 4.4%, respectively). Comparative studies indicated that the incidence rates/year of ECF-TSA and US-TSA were significantly higher in Iceland than in Sweden or in Italy (p<0.05). Genetic and putative epigenetic (environmental) factor(s) might account for the high incidence rate/year of ECF-TSA and US-TSA in this country.