PI3K/AKT/mTOR Pathway Aberration And Its Clinicopathological Significance In Esophageal Squamous Cell Carcinoma

Aims:Tumor targeted therapy is one of the effective methods for tumor treatment. With the development of high-throughput genome sequencing and screening technologies, PIK3CA gene has been identified to serve as potential therapeutic targets in esophageal squamous cell carcinoma (ESCC). Patients with a variety of different types of tumors have good outcomes after treatment with PI3K/AKT/mTOR pathway inhibitors. Patients with PI3K/AKT/mTOR pathway aberrations were more sensitive to these pathway inhibitors. However, there is no systemic research on PIK3CA gene and PI3K/AKT/mTOR pathway aberrations in ESCC patients right now. In this study, we evaluate PIK3CA gene mutations and amplification as well as PI3K/AKT/mTOR pathway aberrations in Chinese ESCC patients. We want to identify the patients may benefit from PI3K/AKT/mTOR pathway inhibitor, and analyze the clinicopathological characteristics of these patients.Methods:This study included444ESCC patients, who underwent radically resection at our Hospital from2004to2007. Direct sequencing was applied to investigate mutations in exons9and20of PIK3CA in Chinese ESCC patients. Fluorescence in situ hybridization (FISH) was used to detect the amplification status of PIK3CA gene. Expressions of PI3K, p-AKT and p-mTOR were evaluated using immunohistochemistry analysis. The associations of PIK3CA gene mutations and amplification and PI3K, p-AKT and p-mTOR expression with clinicopathological characteristics and clinical outcome were examined. We also analyzed the association between PIK3CA genetic alterations and three protein expressions, as well as the factors associated with prognosis and local recurrence.Results:1. Median survival time of ESCC patients was62months (range4-107), and estimated5-year overall survival(OS) was48.2%. Tumor pathologic stage, lymph node metastasis, tumor embolus, treatment after operation and local recurrence were found to be independently associated with prognosis(P=0.006; hazard ratio(HR)=1.825,95%CI: 1.348-2.470, P<0.001; HR=1.582,95%CI:1.093-2.291, P=0.015; HR=0.664,95%CI:0.496-0.888, P=0.006; HR=12.335,95%CI:8.281-18.374, P<0.001, respectively). Besides, we found tumor pathologic stage, lymph node metastasis, tumor embolus and treatment after operation were independently correlated with local recurrence(P<0.001; HR=1.668,95%CI:1.193-2.334, P=0.003; HR=1.910,95%CI:1.284-2.842, P=0.001; HR=1.523,95%CI:1.080-2.147, P=0.016, respectively).2. Thirty somatic point mutations (30/406,7.4%) were identified in exon9whereas no mutations were detected in exon20. PIK3CA mutations were independently correlated with worse overall survival in the ESCC patients with family history of cancer(HR=12.382,95%CI:2.689-57.011, P=0.001).3. The amplification of PIK3CA was detected in87of409(21.3%) tumor samples. PIK3CA amplification was independently correlated with favorable overall survival in the ESCC patients with treatment and patients of pathologic T3(HR=0.510,95%CI:0.288-0.903, P=0.021; HR=0.482,95%CI:0.258-0.898, P=0.022, respectively).4. The expression of PI3K was detected in42of237(17.7%) normal tissue samples and258of428(60.3%) tumor samples. The PI3K was significantly overexpressed in ESCC tumor specimens compared to normal samples. We identified a significant correlation between PI3K expression and pathologic stage, local recurrence and prognosis (P=0.040,0.014and0.027, respectively). PI3K overexpression was independently associated with higher risk of local recurrence in ESCC patients and increased risk for shorter overall survival in female ESCC patients(HR=1.435,95%CI:1.040-1.979, P=0.028; HR=2.220;95%CI:1.016-4.852; P=0.046, respectively). The expression of PI3K is not correlated to PIK3CA mutations and amplifications in ESCC(rs=0.050, P=0.324; rs=-0.006, P=0.902, respectively).5. The expression of p-AKT was detected in47of237(19.8%) normal tissue samples and165of428(38.6%) tumor samples. The p-AKT was significantly overexpressed in ESCC tumor specimens compared to normal samples. The expression of p-AKT was not correlated with clinicopathological characteristics or clinical outcomes. The expression of p-AKT is not correlated to PIK3CA mutations, amplifications and PI3K expression in ESCC(rs=-0.068, P=0.178; rs=-0.077, P=0.122; rs=0.054, P=0.262, respectively).6. The expression of p-mTOR was detected in113of237(47.7%) normal tissue samples and246of428(57.5%) tumor samples. The p-mTOR was statistically overexpressed in ESCC tumor specimens compared to normal samples. The expression of p-mTOR was not correlated with clinicopathological characteristics or clinical outcomes. The expression of p-mTOR is negatively correlated to PIK3CA amplifications (rs=-0.102, P=0.04), and is positively correlated to PI3K and p-AKT expression in ESCC(rs=0.248, P<0.001; rs=0.108, P=0.025, respectively).Conclusions:Most of ESCC patients have PI3K/AKT/mTOR pathway aberrations. PIK3CA mutations were detected in7.4%ESCC patients, PIK3CA amplifications were detected in21.3%ESCC patients, and the expression of PI3K, p-AKT and p-mTOR were detected in60.3%,38.6%and57.5%ESCC patients. Our study provide the evidence for the research in targeting PI3K/AKT/mTOR signal pathway. PIK3CA mutations and amplification can not result in PI3K overexpression in ESCC. PI3K overespression was independently associated with local recurrence, and PI3K is a potential biomarker for local recurrence and prognosis in Chinese ESCC patients.