Small Intestinal Involvement and Genotype-Phenotype Correlation in Familial Adenomatous Polyposis

Abstract

Background and AimsSmall intestinal involvement in familial adenomatous polyposis (FAP) remains unclarified. We performed capsule endoscopy (CE) and balloon-assisted (BA) endoscopy to analyze small intestinal polyps and their genotype-phenotype correlations in a large cohort of FAP patients. MethodsIn this retrospective study, we performed CE in all 149 FAP patients and BA endoscopy in 74 patients with larger polyps. The prevalence of small intestinal adenoma with high-grade dysplasia and cancer was investigated. Correlation between APC variant and polyp phenotype was analyzed. ResultsMedian patient age was 44 years and 69% were male. Pathogenic germline APC variants were found in 117/136 (86.1%). Overall prevalence and median number of small intestinal polyps were 85.2% (127/149) and 17 (IQR 6-36), respectively. A total of 5318 polyps were detected by CE and all 433 polyps histologically examined were confirmed as adenoma. The number of polyps significantly decreased from the proximal-to-distal tracts. Adenoma with high-grade dysplasia was detected in 26.2% (39/149), and its incidence among the polyps was approximately 1.4% (74/5318). Of these, 14 were intramucosal carcinomas with a prevalence of 5.4% (8/149). The germline APC variant in codon 1251-1580 was significantly correlated with a high number of small intestinal polyps. Multivariate analysis revealed APC variant in codon 1251-1580 and a high number of small intestinal polyps as independent risk factors for adenoma with high-grade dysplasia. Spigelman stage was significantly associated with number of jejunal/ileal polyps and their high-grade dysplasia. ConclusionAmong FAP patients, small intestinal adenoma with high-grade dysplasia was detected in 26.2% and cancer in 5.4%. FAP patients, particularly those with APC variant in codon 1251-1580 and/or high Spigelman stage may require surveillance for small intestinal polyps.