Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/30205
Background and aims: Studies suggest an increased risk for certain cancer types for type 2 diabetes (T2DM) and that these patients have an increased mortality from cancer. However, many of the studies in this area are limited by potential bias. Therefore, we set out to evaluate the incidence of all cancer and site-specific cancer, along with time-trends in cancer incidence as well as post-cancer mortality, among patients with T2DM compared to matched controls.
Materials and methods: We included patients defined by the epidemiologic definition as T2DM in the Swedish National Diabetes Register (NDR) between 1998 through 2012 and followed them through 2014. Each T2DM person was matched to 5 controls based on age, sex and county. The cohort included 457,473 persons with diabetes and 2,287,365 matched controls. All individuals were followed until a site-specific cancer occurrence, death or end of follow-up, whichever came first. Incidence, trends in incidence and post-cancer mortality for cancer were estimated with cox regression and standardized incidence rates.
Results: T2DM had a slightly increased risk for all cancer, HR 1.1 (95% CI, 1.09 to 1.12). For the most common cancer sites we observed the following for incidence rates: Increased risk for colorectal cancer HR 1.20 (1.16 to 1.23) and breast cancer HR 1.05 (1.01 to 1.09), decreased risk for prostate cancer HR 0.82 (0.80 to 0.83), and a non-significant risk of lung cancer HR 1.01 (0.97 to 1.05) for T2DM compared to controls. Of these four cancer sites only lung cancer showed a significant difference in change of risk over time, with a 30% greater increase in incidence over a 10 year period for T2DM compared to controls.
For post-cancer mortality we observed the following: Increased mortality after diagnosis of prostate cancer HR 1.29 (1.25 to 1.35), breast cancer HR 1.25 (1.18 to 1.33) and colorectal cancer HR 1.09 (1.05 to 1.13) in T2DM compared to controls. There was not a significant difference in post-cancer mortality between the groups for lung cancer HR 1.02 (0.98 to 1.06).
The cancer types that T2DM was most associated with an increase in risk were the following: Liver HR 3.31 (3.07 to 3.58), pancreas HR 2.19 (2.06 to 2.32), corpus uterus HR 1.78 (1.68 to 1.88), penis HR 1.56 (1.27 to 1.91), kidney HR 1.45 (1.36 to 1.54), gallbladder and bile ducts HR 1.32 (1.13 to 1.54), stomach HR 1.21 (1.13 to 1.30) and bladder HR 1.20 (1.15 to 1.25). Of these sites, only pancreas cancer and corpus uterus cancer showed a significant difference in change of risk over time, with a 38% greater increase in incidence over a 10 year period for pancreas cancer and a 26% greater decrease for corpus uterus cancer for T2DM as compared to controls.
Of the sites most associated with T2DM, only corpus uterus HR 1.25 (1.13 to 1.37), bladder HR 1.12 (1.06 to 1.19) and colorectal cancer HR 1.09 (1.05 to 1.13) had a significant increase in post-cancer mortality as compared to controls.
Conclusion: All cancer incidence was slightly elevated in patients with T2DM compared to controls. Patients with T2DM have an increased risk of certain cancers as well as lower post-cancer survival. Changes in cancer incidence over time were virtually the same in patients with diabetes compared to controls, with the exception of pancreas, corpus uterus and lung cancer. With rising incidence of diabetes these observations may be of importance and a challenge to improve future diabetes care.
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