Objective      To investigate the correlation of the copy number variation (CNV) of Variation_91720 in PIK3CA gene with the susceptibility of esophageal squamous cell carcinoma (ESCC) in Han population at the Southwest region of China.       Methods      From the Southwest region

149 ESCC patients and 205 healthy controls were selected as the research subjects. The copy number of Variation_91720 in peripheral blood was detected by TaqMan  real-time fluorescence quantitative polymerase chain reaction (qRT-PCR)

while the mRNA expression of PIK3CA gene in tumor tissue and adjacent tissue was detected by SYBR Green-based qRT-PCR.       Results      The copy number distribution of Variation_91720 in the ESCC patients was significantly different from that in the healthy controls (P0.001). The copy number loss of Variation_91720 was found to be a risk factor of ESCC (P0.001

OR=5.617

95%CI=2.750-11.470)

whereas the copy number gain of Variation_91720 was a protective factor (P=0.028

OR=0.419

95%CI=0.193-0.911). In 34 ESCC patients

the PIK3CA mRNA expression was statistically higher in the tumor tissue than in the adjacent tissue (P=0.038)

but there was no significant statistical difference between the PIK3CA mRNA expression and the Variation_91720 CNV  (P=0.066).       Conclusion      The copy number loss of Variation_91720 in PIK3CA gene may increase the susceptibility to ESCC

whereas the copy number gain of Variation_91720 may decrease the susceptibility. Variation_91720 may be a biomarker for high-risk population screening and early diagnosis of ESCC.