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DNA copy number changes in colorectal flat adenomas

ABSTRACT: Background & aim: Flat adenomas form a specific phenotype of colorectal adenomas that has been associated with more severe molecular changes and consequently a more aggressive clinical behavior compared to their polypoid counterparts. In the present study we set out to compare one of the molecular changes most explicitly associated with adenoma to carcinoma progression, i.e. chromosomal instability, between flat and polypoid colorectal adenomas. Methods: Consecutive series of 83 flat and 35 polypoid adenomas were analyzed for DNA copy number changes using a high resolution arrayCGH platform as well as for mutations in the adenomatous polyposis coli (APC) gene. Gene ontology on the genes located on the significantly different regions was performed. Results: Overall, flat adenomas show similar DNA copy number changes as polypoid adenomas. Patterns of DNA copy number changes differed between the two phenotypes with significantly more frequently loss of 5q14.3 and 5q15-q23.3 in flat adenomas, while loss of 1p36.32-p35.3, 10q25.2-q25.3, 17p12 and chromosome 18 were more frequent in polypoid adenomas. The 5q15-q23.3 region harbors the APC locus, therefore mutation status of APC was investigated, showing significantly less mutations in flat adenomas. Pathway analysis and datamining linked the 5q region to inflammation. Conclusion: These results provide evidence that flat and polypoid adenomas have partly overlapping DNA copy number changes, while alterations more specific to flat adenomas have associations with inflammation. Loss of 5q has been associated with aggressive behavior and this could serve as an explanation for a more aggressive clinical behavior of flat lesions.

ORGANISM(S): Homo sapiens

PROVIDER: GSE30479 | GEO | 2012/10/04

SECONDARY ACCESSION(S): PRJNA143465

REPOSITORIES: GEO

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Project description:Desmoid tumors (also called deep or aggressive fibromatoses) are potentially life-threatening fibromatous lesions. Hereditary desmoid tumors arise in individuals affected by either familial adenomatous polyposis (FAP) or hereditary desmoid disease (HDD) carrying germline mutations in APC. Most non-FAP (sporadic) desmoids carry somatic mutations in the beta-catenin gene. Previous studies identified losses on 5q and 6q, and gains on 8q and 20q as recurrent genetic changes in desmoids. However, virtually all genetic changes were derived from sporadic tumors. To investigate the somatic alterations in FAP-associated desmoids and to compare them with changes occurring in sporadic tumors, we analyzed 17 FAP-associated and 38 sporadic desmoids for copy number abnormalities (CNAs) by means of array comparative genomic hybridization and multiple ligation-dependent probe amplification. Overall, the desmoids displayed only a limited number of genetic changes, occurring in 44% of cases. Common gains at 8q (7%) and 20q (5%) were almost exclusively found in sporadic tumors. Frequent common losses were observed within a 700 kb region at 5q22.2, comprising the APC gene (11%), in a 2 Mb region at 6p21.2-p21.1 (15%), and in a relatively large region at 6q15-q23.3 (20%). The FAP-associated desmoids displayed a significantly higher frequency of CNAs (59%) than the sporadic tumors (37%). As predicted by the APC germline mutations among these patients, a relatively high percentage (29%) of the FAP-associated desmoids showed loss of the APC region at 5q22.2, which was infrequently (3%) seen among sporadic tumors. Our data suggest that loss of region 6q15-q16.2 is an important event in FAP-associated as well as sporadic desmoids, most likely of relevance for desmoid tumor progression. Fifty-three fresh frozen tumor samples were collected at four institutes: Center for Human Genetics, University of Leuven, Belgium (21 samples); INSERM U674, Fondation Jean Dausset-CEPH, Paris, France (15 samples); Hospital for Sick Children, Toronto, Canada (13 samples); and the Italian Registry of Hereditary Colorectal Cancer (Dr. L. Bertario, 4 samples). In addition, DNA of two fresh frozen tumors, HDD-H of patient III:2 and HDD-I of patient III:6, of our hereditary desmoids disease (HDD) family10 was available (Table 1). In this family, multifocal desmoid tumors were inherited as an autosomal dominant trait, and HDD segregated with a 3' APC mutation at codon 1924. For the latter reason, they were classified as FAP tumors in this study. Three FAP tumors were derived from a family with 2 relatives in the study (D15-1 and D15-2 of a male patient and D16 of his sister). Colonic polyposis had been observed in 12 FAP patients, not in the 2 HDD-FAP patients and not in patient D15. The germline APC mutation was known in 14 of 17 FAP-associated tumors. In 28 of 38 non-FAP-associated desmoid tumors, the beta-catenin gene (CTNNB1) mutation in exon 3 was known and in 1 of 38 tumors an APC mutation was present (data not shown). The remaining tumors were characterized as FAP or non-FAP based on clinical data and positivity of tumor cells upon immunostaining for beta-catenin. DNA was extracted from the tumor samples according to standard methods.

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DNA copy number changes in colorectal flat adenomas

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