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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 15  |  Issue : 2  |  Page : 426-436

Prognostic value of the Epstein–Barr virus and tumor suppressor gene p53 gene in nasopharyngeal squamous cell carcinoma


1 Department of Basic Medical Sciences, School of Basic Medical Sciences, Binzhou Medical University, Shandong, China
2 Department of Medicine, Yantai Yuhuangding Hospital of Qingdao University, Shandong, China
3 Department of Public Health and Management, Binzhou Medical University, Shandong, China

Date of Web Publication1-Apr-2019

Correspondence Address:
Dr. Pengzhou Gai
Department of Medicine, Yantai Yuhuangding Hospital of Qingdao University, Shandong 264000
China
Dr. Xiuzhi Zhou
Department of Basic Medical Sciences, Binzhou Medical University, No. 346 Guanhai Road, Shandong 264003
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcrt.JCRT_750_18

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 > Abstract 


Aims and Methods: Retrospectively, this paper compared the differences of the Epstein–Barr virus (EBV)-encoded small RNAs (EBERs), protein expression and gene mutations of tumor suppressor gene p53 (TP53) in keratinized nasopharyngeal squamous cell carcinoma (KNSCC) and nonKNSCC, and the relationships between pathological features and the prognosis of patients were analyzed.
Results: The positive rate of EBERs hybridization and TP53 expressions was 76.3% and 52.2%, respectively, while the mutation rate of TP53 gene was 39.6%. Logistic regression analysis showed direct relationships between the subtypes of nasopharyngeal squamous cell carcinoma (NPSCC) and EBERs-positive, or frequent consumption of pickled food. Overall survival rates of patients with positive TP53 expression, the TP53 gene mutations, vascular invasions, organ metastases, lymph node metastasis, and clinical recurrence were significantly lower than those of patients without those symptoms. The poorer prognosis was related to regularly drinking and the advanced age. According to the Cox regression analysis, we found that the main prognostic factors of NPSCC patients were the aging, recurrence, TP53 gene mutations, especially exon 7 or 8 mutations.
Conclusions: We concluded that there were the correlations between NPSCC subtypes with EBV infection and frequent intaking of pickled food, while aging, clinical recurrence, and TP53 gene mutations were independent predictors for the poor prognosis of nasopharyngeal carcinoma.

Keywords: Epstein–Barr virus, gene mutations, nasopharyngeal squamous cell carcinoma, prognosis, protein expressions, tumor suppressor gene p53


How to cite this article:
Liu J, Liu Y, Zhang Z, Sun H, Ji X, Li B, Zhou X, Gai P. Prognostic value of the Epstein–Barr virus and tumor suppressor gene p53 gene in nasopharyngeal squamous cell carcinoma. J Can Res Ther 2019;15:426-36

How to cite this URL:
Liu J, Liu Y, Zhang Z, Sun H, Ji X, Li B, Zhou X, Gai P. Prognostic value of the Epstein–Barr virus and tumor suppressor gene p53 gene in nasopharyngeal squamous cell carcinoma. J Can Res Ther [serial online] 2019 [cited 2019 Jun 18];15:426-36. Available from: http://www.cancerjournal.net/text.asp?2019/15/2/426/255105




 > Introduction Top


Nasopharyngeal carcinoma (NPC) is an epithelium-originated malignancy of the nasopharynx, and most pathological type of NPC are squamous cell carcinoma (SCC).[1],[2],[3] Most patients have been at advanced tumors with poor prognosis when being diagnosed.[4],[5] To improve the accuracy of patients' prognosis and guide clinicians to select proper treatment strategies quickly and effectively, it is necessary to identify and screen more molecular markers.

The Epstein–Barr virus (EBV) is an important human oncogenic virus, which is closely implicated in the carcinogenesis of NPC.[3],[6],[7],[8] However, only a few infected-people develop NPC, signifying genetic and environmental factors may be involved.[8],[9],[10] Tumor suppressor gene p53 (TP53) plays an important role in many biological processes, and its gene mutation or protein inactivation leads to the uncontrolled cells growth and the formation of tumors.[11],[12] Studies have shown that the TP53 mutation rate was low; however, the positive rate of TP53 protein expression was high, which may be related to EBV infection and protein inactivation in NPC.[13],[14]

There are still some controversies over the relationships among TP53 mutations, TP53 expressions, and prognosis of NPC. Studies showed that TP53 expressions combining with the regional lymph node metastases can serve as the independent predictors of the recurrence and the short survival time of the patients. However, most of the studies showed that the prognosis of NPC patients was independent of TP53 protein expressions.[15],[16],[17],[18] Recent studies indicated that patients with TP53 gene mutations had a poor ending.[19],[20],[21] Most current studies on TP53 gene mutations from NPC patients were about the polymorphism of codon 72 in exon 4, whereas fewer reports focused on other codon mutations.[15],[16],[22],[23]

According to the latest International Classification Criteria of nasopharyngeal SCC (NPSCC),[24] surgical specimens from NPSCC patients were collected, and the EBV-encoded small RNAs (EBERs) were detected by in situ hybridization (ISH), TP53 protein expressions in tumor cells were detected by immunohistochemistry (IHC) while gene mutations of seven codons in TP53 exon 5-8 were detected by polymerase chain reaction (PCR) amplification and sanger sequencing. Meanwhile, the correlations between the clinical features and EBERs, the protein expressions and mutations of TP53 were analyzed. Furthermore, the effects of EBERs, TP53 gene mutations, TP53 expressions and other clinical factors on NPSCC subtypes and on patients' prognoses were analyzed.


 > Materials and Methods Top


Patients and clinical data

Two hundred and ninety-eight tumor tissues diagnosed with the primary NPSCC by the pathologists were gained after the resection of otorhinolaryngology in the Binzhou Medical University hospital (Yantai, China) and the Yuhuangding Hospital (Yantai, China) from October 2011 to March 2016. All patients who had never received any antineoplastic therapy before the operation signed the written informed consent before the admission and completed the questionnaire on issues including their smoking histories, alcohol consumptions, habits of eating pickled food, family tumor histories and so on.

Resected specimens were checked and selected on the basis of the American National Comprehensive Cancer Network guidelines of 2011. The tissues were fixed by 10% formaldehyde, embedded in paraffin, sliced, and stained with hematoxylin-eosin and IHC, which was diagnosed and classified by two experienced pathologists according to the WHO classification of NPSCC in 1991. NPSCC subtypes comprise NKSCC and NNKSCC.

Ninety-one patients were excluded from the study due to the absence of follow-up information or the inaccurate classification of NPSCC after surgery. Only 207 patients were enrolled in the final study, including 34 cases of keratinized nasopharyngeal SCC (KNSCC) and 173 cases of non-KNSCC (NKNSCC). The study showed that the morbidity rate of male was markedly higher than that of female with a ratio of 16.3%. Moreover, the patients' ages were on average of 60 (range: 16–77) who were all followed up by telephone or hospital clinic. The follow-ups were conducted once every 3 months for the first 2 years and then once every 6 months. By the end of the final follow-up date, all patients have been followed up for >1 year. Overall survival (OS) spanned from the day of the surgery to the day of the death or the last follow-up day. The clinical characteristics of the patients are described as detailed in [Table 1].
Table 1: Patients' characteristics and relationships between Epstein-Barr virus-encoded small RNAs and Tumor suppressor gene p53 gene with pathological features

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In situ hybridization

With digoxin-labeled RNA probes of EBERs, ISH was conducted according to the manufacturer's instructions (no. IHC-6022; Zhongshan Company, Beijing, China). Briefly, the process involves removal of paraffin from 4 to 6 μm slides with xylene, hydration with anhydrous ethanol, dislodging Rnases with gastric enzyme, dehydration with gradient ethanol, hybridization with digoxin-labeled probes, adding anti-digoxigen, staining with diaminobenzidine (DAB), re-staining with hematoxylin, and sealing with neutral balsams. The results showed that the brown-granular substance in the nuclei was positive [Figure 1].
Figure 1: Detection of the Epstein-Barr virus-encoded small RNAs in nasopharyngeal squamous cell carcinoma by in situ hybridization. The Epstein–Barr virus-encoded small RNAs were positive in (b) keratinized nasopharyngeal squamous cell carcinoma and (d) Nonkeratinized nasopharyngeal squamous cell carcinoma and negative in (a) keratinized nasopharyngeal squamous cell carcinoma and (c) Nonkeratinized nasopharyngeal squamous cell carcinoma, ×100

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Immunohistochemistry

All the operating steps were carried out in accordance with the manufacturer's instructions (No. Kit-0010, Max-in, Fuzhou, China). In short, paraffin-embedded sections (2–4 μm) were deparaffinized with xylene, rehydrated with gradient ethanol, antigen replied with citric acid, incubated with antibody, dyed with DAB, stained with hematoxylin, and sealed with neutral balata, respectively. TP53 expressions of the tumor cells were tested by mouse anti-human TP53 monoclonal antibody (clone: DO-7, Mba-0674, Fuzhou, China) which can be selectively combined with the antigenic determinants of the N-terminal region of the protein amino to detect the wild-type TP53 protein and mutant TP53 protein.[15],[25] Results showed that >400 cells were counted in each section, while some necrotic cells and peripheral-colored cells were elided. In a semi-quantitative way, more than 10% of cells were nuclear staining in all cells was defined as TP53-positive expressions, while <10% was TP53-negative expressions [Figure 2].
Figure 2: Representative results of tumor suppressor gene p53 protein expression in nasopharyngeal squamous cell carcinoma by immunohistochemistry. tumor suppressor gene p53 positive expressions were shown in (b) keratinized nasopharyngeal squamous cell carcinoma and (d) Nonkeratinized nasopharyngeal squamous cell carcinoma, and negative expressions in (a) keratinized nasopharyngeal squamous cell carcinoma and (c) Nonkeratinized nasopharyngeal squamous cell carcinoma, ×200

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The analysis of the DNA extraction and the tumor suppressor gene p53 mutations

Tumor tissues in paraffin sections were scraped under the guidance of hematoxylin-eosin staining section and the sample DNA was obtained using AmoyDx paraffin tissue DNA Extraction Kit (AmoyDx FFPE DNA Kit, Amoy Diagnostics, Xiamen, China). The concentration and purity of DNA were detected by spectrophotometer, which was adjusted to no <1 ng/μl. Primers of TP53 Exon 5-8 were designed in accordance with registered documents,[26],[27] and were synthesized by Shanghai United Cell Biotechnology. The PCR reaction was described as follows: A 25 μl reaction volume including 1 μl genomic DNA was used for PCR amplification reaction, and the reaction conditions were as following: 95°C 5 min for one cycle; 95°C 30 s, 55°C 30 s, 72°C 1 min for 30 cycles with a 5 min extension at 72°C. The amplified products were purified and were recycled by 1.5% agarose gel electrophoresis. The sequencing analysis of TP53 exon 5-8 mutation was performed on bidirectional Sanger sequencing by ABI3500Dx gene sequencing (AmoyDx biological medicine technology, Xiamen, China). And then, the sequencing results were compared with the TP53 gene sequences in the gene banks using the Blast software. Standard PCR and sequencing procedures were carried out in accordance with the reported literature.[26],[27]

Statistical analysis

Patients' excel database was established and the relevant statistical analyses were carried out on SPSS software version 17.0 (SPSS Ins., Chicago, IL, USA). All tests were two-sided and P < 0.05 was considered as statistically significant. The associations among clinical features, the TP53 expressions and gene mutations were assessed using the Chi-square tests. Survival rates were worked out and survival curves were drawn by Kaplan–Meier methods while the differences were checked by log-rank test. Logistic regression model was established to analyze the influence of clinical factors on pathological subtypes of NPSCC. Meanwhile, the Cox proportional hazards model was applied in analyzing the correlation between the various clinical features and the postoperative survival of patients through a forward stepwise method with an entered and removed a significant level of 0.05.


 > Results Top


The relationships between the Epstein-Barr virus-encoded small RNAs, tumor suppressor gene p53 protein expressions, TP53 gene mutations, and other clinical features in nasopharyngeal carcinoma

Among the 207 patients, EBERs were detected in 158 patients with a positive rate of 76.3%, which was specifically expressed in elder patients (>60 years old), or patients who drank frequently, or with a history of hypertension, or with larger tumor (>1 cm), vascular invasion, clinical recurrence, TP53-positive expression, TP53 mutations, or NKNSCC subtype [Table 1].

The rate of TP53-positive expressions in NPSCC patients was 52.2%, which was more common in patients without family tumor histories, or with a history of hypertension, or frequently eating pickled food, or with clinical recurrence, TP53 mutations, or with positive EBERs [Table 1].

Mutations of TP53 exon five-eight were detected in 82 of 207 patients (39.6%), and nine mutation patterns were detected on seven codons. Among them, 26 cases occurred on codons 173 of exon 5, 36 cases on exon seven, and 20 cases on exon 8. 58.5% of mutations were G: Cer: A substitutions, followed by gene deletion mutations (26.8%), whereas G: Chi: G and A: Tnd: C substitutions accounted for only 7.3% (only six cases), respectively [Figure 3] and [Table 2]. TP53 gene mutations were more common in patients who ate pickled foods frequently, or patients with a history of hypertension, nerve invasion, vascular invasion (P = 0.020), positive TP53 expressions, positive EBERs, or NKNSCC subtype [Table 1].
Figure 3: Tumor suppressor gene p53 gene mutations of Exon 5-8 in nasopharyngeal squamous cell carcinoma by Sanger sequencing. (a) for codon 173 of Exon 5, (b-d) for codon 241 (b), 249 (c), 261 (d) of Exon 7, and (e-i) for codon 278 (e and f), codon 280 (g), and codon 282 (h and i) of Exon 8

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Table 2: Tumor suppressor gene p53 mutation pattern of 207 patients

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The correlations between clinical variables and nasopharyngeal squamous cell carcinoma subtypes

Various clinical factors were considered in the logistic regression model to analyze their relationships with different pathological subtypes of NPSCC. Univariate analysis revealed that NPSCC subtypes were related to the habits of frequently eating pickled foods (P = 0.020), the habits of drinking frequently (P = 0.045), the TP53 mutations (P = 0.040), or EBERs positive (P < 0.001). Multivariate analysis showed that EBV infection (P = 0.003) and the habits of frequently eating pickled food (P = 0.035) were risk factors for poor-differentiated NKNSCC. NPSCC subtypes were not associated with TP53 gene mutations and protein expressions and other clinical factors, such as gender, hypertension histories, family tumor histories, smoking habits, alcohol consumption, and tumor sizes [P > 0.05; [Table 3].
Table 3: Relationship between clinical characteristics and nasopharyngeal squamous cell carcinoma histological subtypes

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Survival analysis of the nasopharyngeal squamous cell carcinoma patients

By the end of the follow-up which was on an average 37.6 months ranging from 17.8 months to 67.8 months, there were 59 deaths accounting for 28.5%. The 1 year, 3-year, and 5-year OS rate of the patients were 100%, 85.8%, and 56.5%, respectively.

The OS rates of patients with TP53 gene mutations were lower than those of patients without gene mutations with a 3-year rate of 96.2% and 5-year rate of 75.2% (P < 0.001). The patients were regrouped according to exon mutations, and results showed that the 3-year (85.0%, 53.8%, and 88.9% vs. 96.2%), and 5-year (33.1%, 35.3%, and 14.8% vs. 75.2%) survival rate of patients with mutations of exon 5, exon 7, or exon 8 were significantly lower than those of patients without them (P < 0.001). We also regrouped the patients based on whether they are with exon 5, exon 7, or exon 8 mutations or not. The results showed the survival rates of patients with exon 7 or exon 8 mutation were significantly lower than those of without exon seven (3- and 5-year OS: 53.8 and 35.3 vs. 93.8 and 61.5; P < 0.001) or exon 8 (3- and 5-year OS: 88.9 and 14.8 vs. 86.1 and 61.8; P < 0.001) mutations, while there were no differences in OS rate of patients with or without exon five mutations (P = 0.060). With a 3-year rate of 75.4% and 5-year rate of 41.7%, the OS rates of patients whose TP53 expressions were positive were obviously lower than those of patients whose TP53 expressions were negative with a 3-year rate of 97.2% and 5-year rate of 73.0% [P = 0.004; [Figure 4].
Figure 4: Survival analysis of tumor suppressor gene p53 gene mutation and protein expression with overall survival. Overall survival for patients (b) with different exon mutations of tumor suppressor gene p53, with or without (a) tumor suppressor gene p53 gene mutations, (c) exon 5 mutations, (d) exon 7 mutations, (e) exon 8 mutations, (f) positive expression of tumor suppressor gene p53 protein

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The survival rates of patients over 60s with a 3-year rate of 80.9% and 5-year rate of 38.3% were lower than that of patients under 60s with a 3-year rate of 92.2% and 5-year rate of 71.8% (P < 0.001). The OS rates of patients with a habit of regular drinking (P = 0.006), or vascular invasion (P = 0.005), or lymph node metastasis (P = 0.025), organ metastases (P = 0.001), and clinical recurrence were significantly (P < 0.001) lower than those of patients without them. However, the patients' survival rates were not related with EBERs and NPSCC subtypes [P = 0.050 and P = 0.184, respectively; [Figure 5].
Figure 5: Survival analysis of other features with overall survival. Overall survival for patients with (a) negative or positive the Epstein–Barr virus-encoded small RNAs, with different (b) histological subtypes, (c) age groups, with or without (d) drinking regularly, (e) vascular invasion, (f) lymphatic metastasis, (g) organ metastasis, (h) clinical recurrence

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Cox regression model was established to analyze the influence of clinical variables on the prognosis of the patients. Univariate analysis showed that the postoperative outcomes of the patients were greatly affected by the clinical variables including ages (P = 0.001), drinking habits (P = 0.008), vascular invasions (P = 0.007), lymph node metastasis (P = 0.028), organ metastases (P = 0.001), recurrence after surgery (P < 0.001), TP53 protein expressions (P = 0.005) and TP53 gene mutations (P < 0.001), while other clinical factors had no effect on the outcomes, such as gender, hypertension histories, family tumor histories, smoking habits, intaking of pickled foods, tumor size, nerve invasions, EBERs, and NPSCC subtypes (P > 0.05). Meanwhile, multivariate analysis showed that the aging (P = 0.001), recurrence (P = 0.003), and the TP53 gene mutations (P < 0.001) were the independent predictors of NPSCC patients' survival after surgery. Mutations of TP53 exons were included into Cox analysis as variables, and the results suggested that patients with the mutation of TP53 exon seven (P = 0.024) or 8 (P = 0.030) had a poor prognosis after the surgery [P < 0.001; [Table 4].
Table 4: Univariate and multivariate analysis of overall survival time of nasopharyngeal squamous cell carcinoma patients

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 > Discussion Top


EBV plays an important part in the pathogenesis of NPC with different infection rates in different pathological subtypes.[1],[6],[7] Our results showed the positive rate of EBER was 78%, while the positive rates of NKNSCC and KNSCC were 80.9% and 52.9%, respectively. Logistic univariate and multivariate analysis indicated that EBERs was associated with NPC pathological subtypes. Our results suggested that EBV infection was present in all subtypes of NPC, while the infection rate in NKNSCC was significantly higher than that in KNSCC, which were consistent with previous reports.[6],[7]

Studies have shown that EBV components can be used as biomarkers for evaluating prognosis and new targets for the early diagnosis and treatment of NPC patients.[28],[29] Yao et al. announced that patients with lower serum EBV-DNA copies had a better prognosis.[28] A case-control study revealed that advanced NPC patients with EBER-positive had inferior outcomes than those with EBER-negative.[29] However, it was reported that EBER-positivity predicted superior prognosis, especially a long-term (>10 years) follow-up research, and proposed that EBERs-positive were more common in NKNSCC which were more sensitive to clinical radiochemotherapy.[30] Our research showed that although the OS of EBERs-negative patients was longer than that of EBERs-positive patients, EBER was not associated with the patients' prognosis. However, our results also have some limitations. The size of the sample was small, and all specimens were NPC, of which NKNSCC accounted for 83.6%. Therefore, a further study with large number of all NPC subtypes is necessary.

Wild-type TP53 protein is a stress-responsive protein, and stable and complete TP53 gene plays an important role in many biological processes.[11],[31],[32] TP53 has the highest mutation rate of 50%–70% in the sporadic solid tumors, with different tumors harbor, different gene mutation rates and patterns.[22],[33],[34] Meanwhile, TP53 overexpression occurs in all types of tumor,[13],[15] while abnormal expression of TP53 protein often exists in tumor tissues.[12] High protein expression was common in all types of NPC, while the TP53 gene mutation was a rare event.[14],[17],[35] Previous studies have discovered that EBV infection can cause the TP53 protein overexpression by improving the stability of the TP53 protein in NPC, and EBERs and TP53 protein were coordinately expressed in EBV-positive NPC.[13],[14],[36],[37],[38] In this study, the positive rate of TP53 expressions was higher than that of TP53 gene mutations. Of the 108 patients with overexpression of TP53 protein, 80 had TP53 gene mutations, and the others were EBERs positive. The positive rate of TP53 protein was high in EBERs-positive patients, which was low in EBERs-negative patients. Of the patients, TP53 gene mutation were detected in 80 out of 108 patients with positive TP53 protein expression, while EBERs was positive in the other 28 patients with TP53 protein positive and TP53 gene mutation negative. The positive rate of TP53 protein in EBERs positive specimens was high, and the negative rate of TP53 protein in EBERs negative samples was low. TP53 gene mutation, TP53 protein expression and EBERs were co-positive in 80 patients and co-negative in 49 cases. TP53 antibody in this study can be selectively associated with the N-terminal region of TP53 protein, which can be combined with wild-type and mutant of TP53 proteins.[15],[25] In a word, the positive expression of TP53 protein may be related to the TP53 gene mutation and the EBV infection, which also proved that our researches were consistent with the reported literatures.[13],[36],[37],[38]

Research showed that there were no direct correlations between the TP53 protein expressions and the prognosis of NPC.[15],[25] Studies found that patients with positive expressions of TP53 protein and lymphatic metastases had a poor prognosis while TP53 expressions cannot be used as an independent predictor.[15] A study by Ma et al. found that although patients with TP53 positive expressions had a short progression-free survival, TP53 can still not be served as the independent predictors.[16] Our findings suggested that there were radical differences in survival rates between patients with TP53 positive expressions and patients with TP53-negative expressions. Univariate Cox analysis showed that the TP53 expressions can affect the patient's outcome. However, in multivariable analysis, TP53 expressions were not an independent predictor of NPSCC prognosis.

Recent studies on the influence of TP53 gene mutations on the occurrence of NPC and on the prognosis of the patients were mainly focused on codon 72 polymorphism in exon 4 through restriction fragment length polymorphic PCR technology, however, seldom on other codons.[10],[15],[39] Mutation patterns of seven codons in TP53 exon 5-8 were detected through Sanger sequencing in this research. TP53 gene mutations were included in regression analysis as a variable, which showed that there was no direct correlation between the TP53 gene mutations and the pathological type of NPSCC. TP53 gene mutations were included in regression analysis, and results suggested that TP53 gene mutation had no correlation with NPSCC histologic subtypes. However, patients with TP53 gene mutations had a higher recurrence rate of 53.3%, and a poor prognosis with a 3-year survival rate of 82.6% and a 5-year survival rate of 46.1%. Regression analysis revealed that the TP53 gene mutation was an independent predictor of the prognosis of NPSCC patients, which were in line with the previously reported literature.[15] Mutations of TP53 exons as variables were included into Cox analysis, and the results suggested that patients with mutations in TP53 exon seven or eight have a poor prognosis, and can be served as independent predictors of NPSCC patients. This may be related to the fact that mutations in TP53 exon 7 or 8 can cause gene sequence or structural changes and TP53 protein inactivation, which induced the tumor development. Because this finding has not been reported in current documents,[22],[34],[40] our results can provide new evidence for early diagnosis and targeted therapy of NPC. Numerous studies have confirmed that the pathological classification of NPC can be used as a predictor of prognosis, on account of different reactivity among different subtypes.[41],[42],[43] The study showed that although the survival rates of KNSCC and NKNSCC were close in the short term, the survival rates of patients with NKNSCC were slightly higher than those with KNSCC. However, the pathological classification of NPSCC was not related to the prognosis of patients, which was inconsistent with previous literatures.[41],[42],[43] This may be related to the relatively short follow-up timely, and hence, a further long-time study is still necessary.

Moreover, studies showed that the environmental factors had a great effect on the pathogenesis of NPC patients.[1],[44],[45] Frequent intaking nitrosamines carcinogens produced during food pickling is susceptible to NPC.[45] In this study, patients who ate salted food regularly were vulnerable to poor differentiated NPSCC, and logistic analysis also revealed that NPSCC subtypes were related to the habits of frequent ingestion of pickled food. It may be related to the malignant transformation of nasopharyngeal epithelial cells caused by nitrite transported into nasopharyngeal mucosa in vivo, which may be one of the factors leading to familial aggregation in high incidence areas.[1],[44],[45]

Since all the patients enrolled in this study were NPSCC, selection bias may exist and affect the final results. Meanwhile, because this study was a retrospective analysis, the conclusion may be more or less limited. In addition, the limited sample size and a large gap in the gender distribution may also affect the results. Therefore, there are still some drawbacks in this study which can be improved by the larger sample of TP53 mutations from NPC patients in the future.

Retrospectively, this paper detected the EBERs, the TP53 protein expressions and TP53 gene mutations and analyzed their correlations with various clinical factors from NPSCC patients. Meanwhile, the relationships between the variables and NPSCC subtypes and patients' prognoses were also discussed. Our results showed NPSCC subtypes were related to EBV infection and frequent consumption pickled food, but not related to TP53 protein expressions and gene mutations. What's more, aging, clinical recurrence, TP53 gene mutations, especially the mutation of TP53 exon seven or eight can serve as the independent predictors of patients' prognosis.


 > Conclusion Top


Previous reports have shown that there was a relationship between EBV infection and TP53 protein expression.[12],[13],[14] However, there are no comprehensive reports on the roles of EBV infection, TP53 protein expression and TP53 gene mutation in the diagnosis of NPC.

Acknowledgment

This present study was funded by the grant from the Science and Technology Program of Shandong Province (grant no. J15 LK02), and Scientific Research Project of Yantai (grant no. 2016ZH081).

Financial support and sponsorship

The study was financially supported by the Science and Technology Program of Shandong Province (2015J15LK02) and Scientific Research Project of Yantai (grant no. 2016ZH081).

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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