Background In the past decade, cancer has overtaken cardiovascular disease as the leading cause of death among people with type 2 diabetes (T2D) in the UK. Extensive epidemiological evidence suggests T2D is associated with an elevated cancer risk. The association between T2D and site-specific cancers in Scotland was last described for the period 2001–2007. This retrospective cohort study aims to evaluate the impact of T2D on the risk of six site-specific cancers (colorectal, hepatocellular, pancreatic, lung, breast, and prostate) in Scotland between 2008 and 2018.

Methods This retrospective cohort study identified people aged 55–79 years with incident T2D in the national diabetes register between 2008 and 2018. Cancer incidences were ascertained via linkage of the diabetes register to the Scottish cancer registry. A comparison group of individuals aged 55–79 years between 2008 and 2018 not diagnosed with T2D was identified using population data from the National Records of Scotland. Incident cancers for the comparison group were ascertained using cancer incidence data from Public Health Scotland. Directly age-standardised incidence rates by cancer site and sex were calculated using the 2013 European Standard Population. Standardised incidence ratios (SIR) and 95% confidence intervals (CI) assessed the association between T2D and the six site-specific cancers.

Results This study identified 139,769 individuals with T2DM, followed for a median of 3.29 years. A total of 4,075 and 2,600 cases of cancer across all six sites occurred in men and women with T2DM, respectively. Among men, T2D was associated with significantly increased colorectal (SIR 1.26, 95% CI 1.11–1.42), hepatocellular (1.85, 1.43–2.36), pancreatic (2.46, 2.00–3.00), and lung (1.15, 1.02–1.29) cancer risks, but a non-significantly decreased prostate cancer risk (0.94, 0.85–1.04). Among women, T2D was associated with significantly increased colorectal (1.36, 1.16–1.58), pancreatic (4.17, 3.41–5.04), and lung (1.37, 1.22–1.54) cancer risks and non-significantly increased breast (1.11, 0.99–1.23) and hepatocellular (1.16, 0.64–1.93) cancer risks.

Conclusion The association between T2D and cancer in Scotland varies depending on the cancer site. Further research could better characterise these associations following more rigorous adjustment for confounders and investigate potential detection and reverse causation biases. Effective policies to reduce cancer risk among people with T2D are required.