Diabetes can increase the prevalence of EBV infection and worsen the prognosis of nasopharyngeal carcinoma.

Epstein‒Barr virus (EBV) infection is a primary oncogenic factor of nasopharyngeal carcinoma (NPC) that elicits epithelial-mesenchymal transition (EMT). Although diabetic patients are more susceptible to various infectious diseases, the pathological association with virus-related NPC has not yet been clarified. Herein, we evaluated the influence of diabetes on the clinicopathological changes of 70 patients with NPC. Disease-specific survival (DSS) modified by viral infection was also analysed. The proportion of NPC patients with diabetes was 32.9% (23/70 cases), and 91.3% (21/23 cases) were infected with EBV detected by EBER-I in situ hybridisation. NPC with diabetes showed an effect on EMT evaluated by immunostaining for E-cadherin and vimentin, which was correlated with HbA1c levels. Receiver operating characteristic (ROC) curve analysis determined a HbA1c level of 6.5% as the cut-off value for primary disease death at 2 years [area under the curve (AUC) 0.76; sensitivity 0.64; and specificity 0.81]. High HbA1c levels (≥6.5%) significantly increased the number of lymph node metastases in NPC compared to low HbA1c levels (<6.5%, p<0.01). Diabetic NPC patients had a significantly poorer prognosis than all non-diabetic patients (DSS, 72 months vs not reached, p<0.05). Diabetic EBV-positive NPC patients had a significantly poorer prognosis than non-diabetic EBV-positive patients (DSS, 35 months vs not reached, p<0.01). Multivariate analysis using the Cox proportional hazards model also suggested that HbA1c ≥6.5% was a significant factor in poor prognosis, with a hazard ratio of 6.84 (p<0.05). Collectively, our results revealed for the first time a high prevalence of EBV infection, poor prognosis and the importance of proper glycaemic control in diabetic NPC patients.