Integrated genetic and epigenetic analysis of cancer‐related genes in non‐ampullary duodenal adenomas and intramucosal adenocarcinomas

Abstract

The molecular and clinical characteristics of non-ampullary duodenal adenomas and intramucosal adenocarcinomas are not fully understood because they are rare. To clarify these characteristics, we performed genetic and epigenetic analysis of cancer-related genes in these lesions. One hundred and seven non-ampullary duodenal adenomas and intramucosal adenocarcinomas, including 100 small intestinal-type tumors (90 adenomas and 10 intramucosal adenocarcinomas) and 7 gastric-type tumors (2 pyloric gland adenomas and 5 intramucosal adenocarcinomas), were investigated. Using bisulfite pyrosequencing, we assessed the methylation status of CpG island methylator phenotype (CIMP) markers and MLH1. Then using next-generation sequencing, we performed targeted exome sequence analysis within 75 cancer-related genes in 102 lesions. There were significant differences in the clinicopathological and molecular variables between small intestinal-and gastric-type tumors, which suggests the presence of at least two separate carcinogenic pathways in non-ampullary duodenal adenocarcinomas. The prevalence of CIMP-positive lesions was higher in intramucosal adenocarcinomas than in adenomas. Thus, concurrent hypermethylation of multiple CpG islands is likely associated with development of non-ampullary duodenal intramucosal adenocarcinomas. Mutation analysis showed that APC was the most frequently mutated gene in these lesions (56/102; 55%), followed by KRAS (13/102; 13%), LRP1B (10/102; 10%), GNAS (8/102; 8%), ERBB3 (7/102; 7%), and RNF43 (6/102; 6%). Additionally, the high prevalence of diffuse or focal nuclear β-catenin accumulation (87/102; 85%) as well as mutations of WNT pathway components (60/102; 59%) indicates the importance of WNT signaling to the initiation of duodenal adenomas. The higher than previously reported frequency of APC gene mutations in small bowel adenocarcinomas as well as the difference in the APC mutation distributions between small intestinal-type adenomas and intramucosal adenocarcinomas may indicate that the adenoma-carcinoma sequence has only limited involvement in duodenal carcinogenesis.

Small Bowel Epithelial Precursor Lesions: A Focus on Molecular Alterations

“…While little is known on the molecular features of jejunal or ileal adenomas, the most frequent genetic alterations of intestinal-type NADAs involve APC and KRAS genes, similar to colorectal adenomas [ 15 , 16 ]. In a recent study, Ota et al performed integrated genetic and epigenetic analysis of 107 NADAs and intramucosal adenocarcinomas, comprising 100 intestinal-type neoplasms (90 adenomas, 10 carcinomas) [ 16 ]. Their molecular analysis showed that APC was the most commonly mutated gene (55%), followed by KRAS (13%).…”

“…Overall, Wnt/β-catenin signaling pathway has been reported to be dysregulated in NADAs [ 15 , 16 , 17 , 18 ]. Ota et al found APC mutation in 53%, 59%, and 60% of low grade intestinal-type NADAs, high grade intestinal-type NADAs and intestinal-type intramucosal adenocarcinoma, respectively [ 16 ]. Most APC mutations are nonsense or frameshift mutations, mainly distributed in the mutation cluster regions (between codons 700 and 1200 or between codons 1400 and 1600), though a few missense mutations have also been identified.…”

“…Most APC mutations are nonsense or frameshift mutations, mainly distributed in the mutation cluster regions (between codons 700 and 1200 or between codons 1400 and 1600), though a few missense mutations have also been identified. The two more common mutational hotspots within APC gene in NADAs are T1556fs and R1450X [ 16 , 19 ]. Alterations in mutational cluster regions seem to be more common in intestinal-type NADAs (86%) in comparison with intestinal-type intramucosal adenocarcinomas (33%) [ 16 ].…”

“…The two more common mutational hotspots within APC gene in NADAs are T1556fs and R1450X [ 16 , 19 ]. Alterations in mutational cluster regions seem to be more common in intestinal-type NADAs (86%) in comparison with intestinal-type intramucosal adenocarcinomas (33%) [ 16 ]. In addition, APC alterations have been found to be rarer in advanced duodenal carcinomas [ 8 , 9 , 10 , 11 , 19 , 20 ], suggesting that most NADAs have a low potential for malignant progression to duodenal adenocarcinomas and that the adenoma-carcinoma sequence may play a small role in the development of invasive duodenal adenocarcinomas.…”

“…Several studies found a high prevalence (64–90%) of extensive or focal nuclear β-catenin expression in intestinal-type NADAs, as well as alterations in Wnt pathway components, indicating the relevance of Wnt signaling for the development of NADAs [ 15 , 16 , 17 , 18 ]. Among intestinal-type NADAs, the prevalence of β-catenin accumulation does not seem to significantly differ between low grade and high-grade lesions, even if Niwa et al [ 17 ] observed that nuclear β-catenin was more frequent in high-grade lesions and larger size (>20 mm in diameter) NADAs (93%), which are associated with a higher risk of progression to adenocarcinoma [ 5 ].…”