Analysis Of TP53 Gene Mutation And Its Intratumor Heterogeneity In Esophageal Squamous Cell Carcinoma

Objective: Esophageal cancer is one of the most common cancer in the world. Esophageal squamous cell carcinoma(ESCC) is the predominant type of esophageal cancer in the Chinese population, with high incidence and mortality. Late-stage ESCC patients usually have unfavorable outcomes. Currently, understanding the mechanisms of tumorigenesis and development of ESCC remains limited. TP53, one of the most important tumor suppressor genes, plays important roles in the maintenance of genomic stability, as well as the regulation of cell proliferation and apoptosis. TP53 mutations were detected in the vast majority of human cancers, however, little evidence has been reported on the intratumor heterogeneity of TP53 mutations. In this study, we investigated the status of TP53 gene mutations and its intratumor heterogeneity in ESCC. This study might provide theoretical basis for tumorigenesis and development of ESCC, as well as the individual diagnosis and treatment.Methods: We collected the surgical specimens from 30 ESCC cases. For each case, one morphological normal surgical margin and four spatially separated tumor specimens were obtained from each individual(with each section at least 0.5 cm away from the others), labeled as N, 1T, 2T, 3T and 4T. Polymerase chain reaction(PCR) and Sanger sequencing were performed on the exons 2~11 of TP53 gene. The relationship between TP53 gene mutations and the clinic-pathological parameters as well as the intratumor heterogeneity of TP53 gene mutations were analyzed.Results: The results showed that TP53 mutations were present in 60%(18/30) of ESCC patients, including 16 cases with point mutations(three with nonsense mutations and thirteen with missense mutations), and two with deletion mutations. Most mutations were detected within exons 5~8 of TP53 gene. 23.3%(7/18) of the mutations affected exon 5, with the highest mutation rate, while mutations in exons 6, 7, 8 and 10 occurred in 3, 2, 4 and 2 cases. Mutations in codon 282(R282W) and codon 175(R175H) were detected in 2 and 3 cases, respectively. We next analyzed the ratio of the peak height of mutant allele compared to the normal one, which was referred to as the relative intensity(RI). In the 16 cases with TP53 mutations, great differences were observed between the RI values of 4 tumor regions in 12 cases.Conclusions: Our data showed a high frequency of TP53 gene mutations and intratumor heterogeneity in ESCC, and no correlations were found between TP53 gene mutations and the clinic-pathological parameters.