Type 2 Diabetic Mellitus Is a Risk Factor for Nasopharyngeal Carcinoma: A 1:2 Matched Case–Control Study

BACKGROUND: Diabetes has been identified as an adverse prognostic variable which associated with an increased mortality in various cancers, including colorectal, lung, and breast cancers. However, previous studies provided inconsistent results on the association between diabetes and nasopharyngeal carcinoma (NPC). The main aim of this study was to investigate the associations between diabetes mellitus and the survival of NPC patients. METHODS: This study was designed as a 1:2 matched case–control study. Cases were patients who met the criteria for the diagnosis of type 2 diabetic mellitus (DM) below. Controls, matched 1:2, were patients who were normoglycemic (NDM). The survival rates were assessed by Kaplan–Meier analysis, and the survival curves were compared using a log-rank test. Multivariate analysis was conducted using the Cox proportional hazard regression model. RESULTS: Both locoregional relapse-free survival (LRRFS) and disease-free survival (DFS) in the NDM group were higher than that in the DM group (p = 0.001 and p = 0.033). Additionally, subset analyses revealed that the differences in OS, LRRFS, and DFS were all significant between the two groups in the N0-N1 subset (p = 0.007, p =.000 and p = 0.002). The LRRFS was higher in the NDM group in the III-IV, T3-T4 and N0-N1 subsets (p = 0.004, p = 0.002 and p =.000). In T3-T4 subset, the NDM group experienced higher DFS than the DM group (p = 0.039). In multivariate analysis, T stage and N stage were found to be independent predictors for OS, DMFS and DFS; chemotherapy was a significant prognostic factor for DMFS and DFS, age for OS, and diabetes for LRRFS and DFS. CONCLUSIONS: Type 2 diabetic mellitus is associated with poorer prognosis among patients with NPC.