For patients with cancer, prevalent type 2 diabetes at the date of cancer diagnosis is associated with increased cancer-specific and all-cause mortality (1,2). Yet, despite potential health implications, there is limited knowledge on whether cancer is also a risk factor for type 2 diabetes. Moreover, the impact of new-onset type 2 diabetes after cancer diagnosis on survival among cancer patients is unknown. We investigated the incidence of type 2 diabetes following a cancer diagnosis and evaluated the influence of new-onset type 2 diabetes in patients with cancer on overall survival.
We included 51,353 incident cancer case subjects diagnosed from 2004 to 2015 living in the Greater Copenhagen area without type 2 diabetes, defined according to one measurement of plasma or serum glucose ≥11 mmol/L or HbA1c ≥6.5% (48 mmol/mol), at diagnosis, each with 10 cancer- and type 2 diabetes–free age- and sex-matched control subjects. In Denmark, health care is public and free for all residents. We sampled all 112 million tests from 1.3 million individuals, performed by the Copenhagen General Practitioners’ Laboratory, contained in the Copenhagen Primary Care Laboratory Database (CopLab) (2015-57-0121) from 2000 to 2015, data for which were merged with data on incident cancer from the Danish Cancer Registry. Only cancer types with >1,000 incident cases with individuals aged >30 years were included. Individuals with diabetes prior to the cancer diagnosis were excluded. The median follow-up time was 2.34 years (interquartile range 0.70–5.53) for all case subjects and 4.41 years (2.04–7.40) for cancer-free control subjects.
We found an increased hazard of new-onset type 2 diabetes for all cancers (hazard ratio [HR] 1.09; 95% CI 1.03–1.14) (Fig. 1A). The hazard of new-onset type 2 diabetes for different cancer types in comparisons with control subjects was particularly strong for pancreatic cancer (HR 5.00; 95% CI 3.62–6.90), cancer of the brain and other parts of the nervous system (HR 1.54; 95% CI 1.22–1.95), and cancer of the corpus uteri (HR 1.41; 95% CI 1.10–1.84).
Having established an increased hazard for incident type 2 diabetes in patients with specific cancer types, we next investigated whether new-onset type 2 diabetes following cancer diagnosis influenced survival. To this end, we considered a subpopulation of 28,308 cancer patients who were still alive 2 years after diagnosis. Compared with cancer patients without type 2 diabetes, cancer patients with new-onset type 2 diabetes in this 2-year period had a 21% higher all-cause mortality (HR 1.21; 95% CI 1.04–1.41) (Fig. 1B).
To our knowledge, this study is the largest cohort study addressing the effect of cancer on the risk of subsequent new-onset type 2 diabetes in adults. This advantage comes from the use of a large amount of high-quality data in combining a clinical database with information from population-based registries containing information on all residents in the catchment area free of selection or recall bias..