A national observation study of cancer incidence and mortality risks in type 2 diabetes compared to the background population over time

Abstract

We examined changing patterns in cancer incidence and deaths in diabetes compared to the background population. A total of 457,473 patients with type 2 diabetes, included between 1998 and 2014, were matched on age, sex, and county to five controls from the population. Incidence, trends in incidence and post-cancer mortality for cancer were estimated with Cox regression and standardised incidence rates. Causes of death were estimated using logistic regression. Relative importance of risk factors was estimated using Heller's relative importance model. Type 2 diabetes had a higher risk for all cancer, HR 1.10 (95% CI 1.09-1.12), with highest HRs for liver (3.31), pancreas (2.19) and uterine cancer (1.78). There were lesser increases in risk for breast (1.05) and colorectal cancers (1.20). Type 2 diabetes patients experienced a higher HR 1.23 (1.21-1.25) of overall post-cancer mortality and mortality from prostate, breast, and colorectal cancers. By the year 2030 cancer could become the most common cause of death in type 2 diabetes. Persons with type 2 diabetes are at greater risk of developing cancer and lower chance of surviving it. Notably, hazards for specific cancers (e.g. liver, pancreas) in type 2 patients cannot be explained by obesity alone.

Figure 1

Causes of death in Sweden between 1998 and 2012. (a) Results for males with type 2 diabetes and controls, (b) results for females with type 2 diabetes and control.

Figure 2

Hazard ratios for cancer incidence, 10-year trends, post-cancer mortality, and cancer specific survival in Type 2 diabetes patients versus matched controls. (Red) Hazard ratios of incidence; (Green) hazard ratios for 10-year trends in incidence; (Blue) hazard ratios for post-cancer mortality for the most common (a) and most associated (b) cancer sites. Incidence model adjusted for sex, education, income, marital status and geographical region of birth. Time trends in incidence were adjusted for age and gender. Post-cancer mortality model adjusted for sex, age, education, marital status and income.

Figure 3

Time trends in cancer incidence. The most common and most associated sites. The x-axes show calendar years from 1998 to 2013. The y-axes display standardised incidence rates (note the differing limits on the y-axes). Blue lines represent people with type 2 diabetes and red lines represent matched controls from the general population. Model was adjusted for sex, education, income and marital status.