The aim of this case-control study was to assess the effect of preexisting diabetes mellitus on the risk of developing non-Hodgkin's lymphoma, and also to investigate whether preexisting diabetes mellitus could further affect survival after diagnosis of non-Hodgkin's lymphoma. The retrospective cohort consisted of 242 study participants with pathologically confirmed non-Hodgkin's lymphoma who were referred to the Department of Radiation Oncology in Chang-Gung Memorial Hospital between January 2000 and March 2004. The controls were derived from a population-based multiple screening program. A logistic regression model was employed to calculate the odds ratios of the risk factors we examined and then to evaluate the association between preexisting diabetes mellitus and the occurrence of non-Hodgkin's lymphoma. The results showed that preexisting diabetes mellitus was an independent risk factor for the occurrence of non-Hodgkin's lymphoma (odds ratio, 1.88; 95% confidence interval, 1.22-2.89; P=0.0045). When subgroup analyses regarding certain tumor or disease characteristics were performed, the impact of preexisting diabetes mellitus was found to be particularly evident in some subgroups such as the tumors of T-cell origin (P=0.0266), those with extranodal involvement (P=0.0346), and those that were not localized or low grade (P=0.0096). The effect of preexisting diabetes mellitus on the risk of death from non-Hodgkin's lymphoma varied with follow-up time. Such an effect modification was statistically significant (P=0.05). In the current study, preexisting diabetes mellitus was an independent risk factor for the occurrence of non-Hodgkin's lymphoma, and it was also an accelerated factor for the risk of death from causes related to non-Hodgkin's lymphoma.

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