Mutation Profiling of Premalignant Colorectal Neoplasia

Accumulation of allelic variants in genes that regulate cellular proliferation differentiation and apoptosis may result in expansion of the aberrant intestinal epithelium generating adenomas. Herein we compared the mutation profiles of conventional colorectal adenomas (CNADs) across stages of progression towards early carcinoma. DNA was isolated from 17 invasive adenocarcinomas (ACs) and 58 large CNADs including 19 with low-grade dysplasia (LGD) 21 with LGD adjacent to areas of high-grade dysplasia and/or carcinoma (LGD-H) and 28 with high-grade dysplasia (HGD). Ion AmpliSeq Comprehensive Cancer Panel libraries were prepared and sequenced on the Ion Proton. We identified 956 unique allelic variants; of these 499 were considered nonsynonymous variants. Eleven genes (APC KRAS SYNE1 NOTCH4 BLNK FBXW7 GNAS KMT2D TAF1L TCF7L2 and TP53) were mutated in at least 15% of all samples. Out of frequently mutated genes TP53 and BCL2 had a consistent trend in mutation prevalence towards malignancy while two other genes (HNF1A and FBXW7) exhibited the opposite trend. HGD adenomas had significantly higher mutation rates than LGD adenomas while LGD-H adenomas exhibited mutation frequencies similar to those of LGD adenomas. A significant increase in copy number variant frequency was observed from LGD through HGD to malignant samples. The profiling of advanced CNADs demonstrated variations in mutation patterns among colorectal premalignancies. Only limited numbers of genes were repeatedly mutated while the majority were altered in single cases. Most genetic alterations in adenomas can be considered early contributors to colorectal carcinogenesis.