Association Of PIK3CA Copy Number Variation With Esophageal Cancer Susceptibility

Objective:Esophageal cancer （EC） is one of the most common malignant tumors inChina,genetic susceptibility and environmental factors play an important role in themechanism ofthe occurrence and development of EC. Recently, copy numbervariation（CNV） has becomea research hotspot in the study of human genetic susceptibilityto some complex diseasesincluding malignant tumor.Additionally, previous studies foundthat PIK3CA genemutation associate with carcinogenesis and development of EC.Ourstudy is aimed toinvestigate the potential association between CNV in PIK3CA and ECsusceptibility,and try to find out the high risk population and early diagnostic biomarker ofEC.Methods:EC patients who were diagnosed by pathology were chosen as case group,and healthy people who were matched in age, gender and region were chosen as controlgroup.Peripheral blood （PB） were drawn to extract genomic DNA （gDNA）. Database ofGenomic Variants （DGV） was used to select Variation₉1720as the candidate loci in thisstudy.Real-time fluorescence quantitative polymerase chain reaction （PCR） based onTaqMan probewas used to detect Variation₉1720copy number （probe is provided byABI）. CopyCaller v2.0software was used to quantitative the copy number. Additionally,EC tumor tissue andadjacent non-tumor tissue paired tissues were used as PIK3CA genemRNA expression quantity analysis object which were obtained from the EC patients whoaccepted esophagectomy. Extract tissue mRNA, and reverse mRNA to cDNA. Real-timefluorescence quantitative PCR based on SYBR Green was used to detect PIK3CA genemRNA expression （probe is designed by Oligo6Demo and Primer Premier5.0software）.The expression of mRNA were calculated by2-Ctquantitative method. SPSS v13.0software was used to statistical analysis for all results.Results:220EC patients（case group） and213healthy people（control group） wereincluded. Tumor and non-tumor tissue paired samples were acquired from47ECpatients（Among them,34pairs were chosen to attend the association analysis between the PIK3CA expression differential and Variation₉1720copy number）. The distribution ofVariation₉1720copy number in EC case group was significantly different from that incontrol group（P<0.001）. EC patients were more than controls with low copy number ofVariation₉1720[P<0.001, odds ratio（OR）=6.575,95%confidence interval（CI）=3.341-12.937], which means that the low copy number of Variation₉1720was a risk factor in ECoccurrence.Furthermore, controls were more than EC patients with high copy number ofVariation₉1720in female population （P=0.038,OR=0.409, CI=0.176-0.951）, which meansthat the high copy number of Variation₉1720was a protect factor in EC occurrence infemale population. Tumor tissues had significantly higher expression level of PIK3CAmRNA than adjacent tissues（P=0.023）.Additionally, we have found a inverse correctionbetween the expression of PIK3CA mRNA （34samples） and copy number ofVariation₉1720（correlation coefficient=-0.319）, but their difference was not so significant（P=0.066）.Conclusion:Low copy number of Variation₉1720in PIK3CA may increase thesusceptibility to EC. Low copy number of Variation₉1720may increase PIK3CA mRNAexpression in tumor tissue. Variation₉1720may be a biomarker for screening of high-riskpopulation and early diagnosis of EC.