Impact of type 2 diabetes on the association between neurodegenerative diseases and cancer in elderly Koreans: a 10-year retrospective cohort study using the National Health Insurance Service Database
Abstract Background Some studies suggest that cancer and type 2 diabetes (T2D), as well as neurodegenerative disease (ND), are related to protein misfolding and possibly to each other. This study aimed to investigate the association between NDs and cancer to evaluate the impact of T2D on the association between NDs and cancer. Methods A population-based 10-year follow-up study was conducted using the Korean National Health Insurance Service Database between 2002 and 2015. The study population included an ND group (n = 9,292) and control group (n = 46,742), aged ≥ 60 years. A multivariable Cox proportional hazards regression model was used to evaluate the hazard ratio (HR) and 95% confidence interval (CI) for cancer risk. Results Various NDs and/or T2D were newly diagnosed in ND and control groups during the 10-year follow-up periods. Newly developed ND cases before cancer onset were 2,412 (26.0%) in the ND group and 15,435 (33.0%) in the control group (χ2 = 178.19, p < 0.01). Newly developed T2D cases before cancer onset were 4,691 (50.5%) and 25,695 (55.0%) in the ND and control groups, respectively (χ2 = 62.89, p < 0.01). As of December 31, 2015 (the end of the observation period), the number of cancer patients in the ND group was 2,040 (22.0%) and that in the control group was 8,628 (18.5%) (χ2 = 61.45, p < 0.01). The ND group was associated with an increased risk of cancer (HR, 1.25; 95% CI, 1.19–1.31). In both groups, newly diagnosed ND and T2D patients showed an additive effect on cancer incidence during the follow-up period. The additional effect on cancer incidence was higher in T2D than in ND. Conclusion This study showed a positive association between NDs and cancer, and an additive effect of T2D on this association. Further replication studies are needed to address the association among NDs, cancer, and T2D.