Quantitative expression analysis and prognostic significance of the BCL2-associated X gene in nasopharyngeal carcinoma: a retrospective cohort study

Abstract

Background: Nasopharyngeal carcinoma (NPC) is a highly metastatic epithelial malignancy showing high prevalence in Southeast Asia and North Africa. The BCL2-associated X (BAX) gene encodes the most important pro-apoptotic member of the BCL2 family. We have recently shown that BCL2 and BCL2L12, two other members of the same apoptosis-related family, possess significant prognostic value in NPC. The objective of the current study was to analyze BAX mRNA expression in nasopharyngeal biopsies of NPC patients, and to assess its prognostic potential in this disease.

Methods: Total RNA was isolated from 88 malignant and 9 hyperplastic nasopharyngeal biopsies, resected from Tunisian patients. After cDNA synthesis by reverse transcription of polyadenylated RNA, BAX mRNA expression was analyzed using a highly sensitive quantitative real-time polymerase chain reaction (qRT-PCR) method.

Results: Lower BAX mRNA levels were detected in NPC biopsies than in hyperplastic nasopharyngeal samples. BAX mRNA expression status was associated with low tumor extent, negative regional lymph node status, and absence of distant metastases. Kaplan-Meier survival analysis demonstrated that patients with BAX mRNA-positive NPC have significantly longer disease-free survival (DFS) and overall survival (OS). In accordance with these findings, Cox regression analysis revealed that BAX mRNA expression can be considered as a favorable prognostic indicator of DFS and OS in NPC, independent of their gender, age, tumor histology, tumor extent, and nodal status. Furthermore, NPC patients without distant metastases are less likely to relapse when their primary tumor is BAX mRNA-positive, compared to metastasis-free patients with a BAX-negative nasopharyngeal malignancy.

Conclusion: This is the first study examining the potential clinical utility of BAX as a prognostic tumor biomarker in NPC. We provide evidence that BAX mRNA expression can be considered as an independent favorable prognostic indicator of DFS and OS in NPC.

Figure 1

Comparison of the distribution ofBAXmRNA expression in malignant nasopharyngeal tumors and hyperplastic nasopharyngeal tissues.BAX transcripts encoding proapoptotic protein isoforms are far less abundant in NPC specimens than in hyperplastic tissue biopsies (P < 0.001). The P value was calculated using the non-parametric Mann–Whitney U test. The dark line near the middle of each box indicates the 50^th percentile (the median value) of each group, the bottom and top of each box represent the 25^th and 75^th percentile, respectively, and whiskers extend to 1.5 times the height of the box; the points represent outliers, while the asterisks show extreme outliers.

Figure 2

Kaplan-Meier curves for disease-free survival (DFS) and overall survival (OS) of nasopharyngeal carcinoma (NPC) patients withBAXmRNA-positive and -negative nasopharyngeal tumors.BAX mRNA expression status possesses a favorable prognostic value in NPC, as patients with BAX mRNA-positive nasopharyngeal tumors have significantly longer DFS (P = 0.001) (A) and OS (P < 0.001) (B), compared to NPC patients with BAX mRNA-negative tumors.

Figure 3

Kaplan-Meier survival curves for NPC patients without distant metastases.BAX mRNA expression status possesses a favorable prognostic value in these patients, as patients with BAX mRNA-positive nonmetastatic nasopharyngeal tumors have a significantly higher probability of DFS (P < 0.001) (A) and OS (P = 0.009) (B) anytime, in comparison with metastasis-free patients bearing BAX mRNA-negative tumors.