IS THERE AN ASSOCIATION BETWEEN CANCER AND DEMENTIA IN COHORTS WITH AND WITHOUT T2DM? A NATIONAL OBSERVATIONAL STUDY

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Previous studies have suggested an inverse association and a hypothesized mutually protective effect between several forms of cancer and late-onset dementia (LOD). Type 2 diabetes (T2DM) is an established important risk factor for both diseases; however, the precise relationships between T2DM, cancer and LOD still remain poorly understood. In this study, we aim to investigate the relationship between different cancers and risk of LOD, and explore the effect of prediabetes or T2DM in these associations. Using the Clinical Practice Research Datalink (CPRD), a massive NHS primary care database, in years, 1998–2015, we identified a sample of individuals ≥ 65 years old, with and without T2DM. Exploratory analyses were performed to investigate the incidence rates of cancer and LOD in both cohorts. Cox proportional hazard models, with time-dependent covariates, were used to determine the risk of LOD in individuals with and without a cancer diagnosis in both cohorts. Separate analyses amongst 217,335 individuals with T2DM and 740,997 without T2DM were performed. The incidence rate of LOD was 8.68 (95 % CI [8.53–8.85]) and 8.84 (95 % CI [8.77–8.92]) per 1,000 person years in the T2DM and non-T2DM cohorts, respectively. Individuals with cancer had a 48 % and 26 % reduction risk of LOD compared to those without cancer in the T2DM and non-T2DM cohorts, respectively. Cancer patients had a decreased risk for LOD [HR=0.67, 95 % CI (0.66–0.68) p<0.01] in the T2DM and [HR=0.50, 95 % CI (0.47–0.53) p< 0.01] non-T2DM cohorts. This inverse association persisted when the outcome of interest was examined with specific forms of cancers. For example, there was a decreased risk for LOD in individuals with bladder cancer in both T2DM [HR=0.52, 95 % CI (0.43–0.63) p<0.01] and non-T2DM cohorts [HR=0.77, 95 % CI (0.72–0.83) p<0.01]. Our results suggest an inverse association between several forms of cancer and LOD independent of T2DM status. In an ageing population, the understanding of biological links between comorbid conditions is imperative to improve our knowledge of biological pathways and mechanisms of common diseases. If further validated our findings may help inform more refined preventative strategies and approaches.