| Background and ObjectiveColorectal laterally spreading Tumor(LST)refers to the superficial tumor lesion larger than 1 cm and extending along intestinal wall.It can be divided into 2 types and 4 subtypes based on surface morphology:granular type(LST-G)including homogeneous G-type(LST-G-H)and nodular mixed G-type(LST-G-MX);non-granular(LST-NG)including flat elevated NG-type(LST-G-F)and pseudo-depressed NG-type(LST-NG-PD).LST is an important type of precancerous lesion.Recent studies revealed that the percentage of high-grade intraepithelial neoplasia(HIGN)and submucosal invasion of LST ranges from 45%to 79%and the risk increases with lesion size.LST with HGIN is known as dangerous pre-cancer lesion due to its great potential of canceration.Because of lack of exclusive cell series,there was little study about its molecular alteration and the mechanism remains unknown.Getting to know the somatic mutation status is an important step to investigate the details of tumorgenesis.Until recently,large scales of studies based on next-generation sequencing have been conducted and revealed numerous mutated genes of human adenocarcinoma.To get a deeper insight into developing mechanism,novel strategies were built to extract mutational signatures from catalogues of somatic mutations revealing the diversity of mutational processes underlying the development of cancer;and to identify key proteins or critical networks.These methods and models have become one of the effective means to recognize the molecular mechanism.Scientists have paid attention to DNA mutations in LSTs as well.Luke B.Hesson et al in Australia performed a genetic analysis of 10 LSTs containing predominantly LGIN lesions and determined a limited number of recurrent mutant genes.We still know little about its genetic alteration,especially somatic mutation of LST with HGIN.Here we performed whole-exome sequencing(WES)on 10 LSTs with HGIN to reveal the somatic mutational landscape.MethodsHere we performed whole-exome sequencing on 10 LST with HGIN and matched adjacent mucosal to call somatic nucleotide variants and base insertion/deletions.We intend to reveal the significantly mutated genes,mutational signature,and its significantly mutated subnetworks.According to the result,we also conducted Sanger sequencing for selected genes in validation series.ResultsWe found 128 recurrently mutated genes.APC gene is the most frequently mutated gene,all of which were inactive mutations,followed by GNAS,TTN FBXW7 and FAT4.We determined 315 significantly mutated genes(SMG),among which 25 known driver genes were detected and over 70%of them harbored inactive mutations.Notably,we identified 2 significantly mutated subnetworks whose components mainly belong to Hippo/TGF-β and cAMP/Rap1/MAPK signaling,indicating their critical role of LST oncogenesis.Meanwhile,we found that a LST-NG lesion harbored the most mutations and signature 6 which has a strong relationship with DNA mismatch repair deficiency.Interestingly,we detected GNAS R186C/H mutation in 40%(4/10)of samples.Then in validation series of 60 LSTs,we found that 10 lesions carried GNAS R186C/H and all of them were rectal villous or tubulovillous adenomas with HGIN.GNAS R186C/H was associated with rectal and villous adenoma(VA).The average size of the LST lesions with GNAS R186C/H was significantly larger than those without it.Collectively,our study can give a comprehensive insight of somatic mutational landscape of LST and provides more clues of its molecular mechanism.ConclusionIn current study,we performed WES on 10 LSTs with HGIN and identified a large number of damaging SNVs and indels.Further analysis revealed 315 significantly mutated genes,special mutational signature profile,altered pathways and 2 statistically significant mutated subnetworks.We found that GNAS R186C/H mutation is commonly seen in LST and correlates strongly with rectal VA lesion.Our study gives a more detailed insight into the somatic mutational landscape of LST and contributes to clarify the complex molecular mechanism. |
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