Clinicopathological and prognostic significance of neuropilin-2 and glioma-associated oncogene homolog 1 expression in esophageal squamous cell carcinoma

Abstract

Background: Esophageal cancer is a deadly cancer which ranked the eighth most common cancer in the world in2012. The two major histological types are squamous cell carcinoma (SCC) and adenocarcinoma with SCC being more prevalent in Asia. Major risk factors of esophageal squamous cell carcinoma (ESCC)are smoking, consumption of alcohol and salty food. Common treatments include esophagectomy, chemotherapy, radiotherapy and targeted therapies. Neuropilin-2 (Nrp2) is a multifunctional transmembrane glycoprotein found in vasculature and tumor cells. It plays important roles in tumor angiogenesis and oncogenesis by acting as co-receptor to modulate functions of other receptorsor by signaling independently. Glioma-associated oncogene homolog 1 (Gli-1) is a transcription factor and an effector of the Hedgehog signaling pathway. Its role in tumor metastasis and tumor stem cell functions has been vastly studied. Overexpression of both proteins with correlation with poor patient survival has been demonstrated in some cancers.

Objectives: Immunoexpressions of Nrp2 and Gli-1 were studied in ESCC clinical specimens. Their expressions were correlated with clinicopathological parameters and patient survival in order to determine their value as prognostic markers in ESCC. Correlation between the two proteins was also studied to evaluate how they were interrelated.

Material and Methods: Patient records from esophagectomy specimens received from 2003 to 2010 were retrieved from the computerized database of Queen Mary Hospital. Patients with prior chemotherapy or radiotherapy directed towards the tumor were excluded. Corresponding paraffin blocks of primary ESCC tissue and metastatic lymph nodes were retrieved for the construction of tissue microarrays (TMAs). Immunohistochemistry was performed on the TMA sections for Nrp2 and Gli-1. Staining intensity was scored with an arbitrary four-point scale and evaluated with the ‘hot spot’ approach. Log-rank test, Mann-Whitney U test, Spearman’s rank test, chi-square test or Fisher’s exact test were used for analysis where appropriate.

Results: The cohort consisted of 76 ESCC patients. Results showed that both Nrp2 and Gli-1 were overexpressed in ESCC compared with normal esophageal tissue. High level of Nrp2 or Gli-1 significantly correlated with poor patient survival (p=0.012 and p=0.047 respectively).High Nrp2 also correlated with shorter metastasis-free survival (p=0.018). Combined high Nrp2 and high Gli-1 was the strongest predictor for poor patient survival compared with high expression of either marker (p<0.001). Cox regression analysis showed that N-stage, M-stage and Nrp2 were all independent prognostic factors in ESCC (p=0.01, p<0.001 and p=0.013 respectively). Correlation analysis showed that while Nrp2 expression was not significantly correlated with any of the clinicopathological parameters, yet high Nrp2 expression correlated with tumor depth, regional lymph node metastasis and lymphatic invasion in some patient subgroups. Gli-1 expression was correlated with gender and metastatic potential (p=0.021 and p=0.043 respectively). Gli-1 and Nrp2 expressions were significantly correlated (p= 0.023).

Conclusion: Expressions of Nrp2 and Gli-1 in ESCC were aberrant indicating their important roles in carcinogenesis and progression of ESCC. High Nrp2 or Gli-1 expressions were significant prognostic indicators for ESCC while only Nrp2 was an independent prognostic factor. The potential of Nrp2 being a therapeutic target in ESCC should be further explored.