A large new observational study from the University of Leicester finds that cancer mortality in people with type 2 diabetes is substantially higher than in the general population. The increase was 18% for all cancers combined, 9% for breast cancer, and 2.4 times for colorectal cancer. Notably, breast cancer mortality was up by 4.1% per year among younger women with type 2 diabetes.
People with diabetes also had around double the mortality rate of the general population from diabetes-related cancers including liver, pancreatic, and endometrial cancers.
The authors said, “Our findings underline the growing cancer burden in people with type 2 diabetes, particularly in older individuals, and highlight the need to prioritize cancer prevention, research, early detection, and management in this population. This is especially true for colorectal, pancreatic, liver, and endometrial cancer, whose mortality rates were substantially higher in individuals with type 2 diabetes than in the general population.”
The research was based on data from the Clinical Practice Research Datalink (CPRD) and looked across a 20-year period from 1998-2018. The team’s work was published in Diabetologia.
Accumulating epidemiological evidence shows people with type 2 diabetes have a higher risk of incidence and mortality for some types of cancer. Prolonged exposure to the effects of increased blood sugar and insulin levels, insulin resistance and chronic inflammation are all potential underlying biological mechanisms. There is also new evidence of a biological link, the protein prostasin, between diabetes and cancer.
Robust evidence indicates a causal relationship between type 2 diabetes and pancreatic, liver, and endometrial cancer. But little is known, overall, about inequalities in cancer mortality rates of diabetics.
In this study, the authors used the CPRD to identify a cohort of individuals aged 35 years or over who had newly diagnosed type 2 diabetes. CPRD is a UK general practice database. The researchers analyzed trends in all-cause, all-cancer and cancer-specific mortality rates by age, gender, ethnicity, socioeconomic status, obesity and smoking status. They also estimated standardized mortality ratios comparing mortality rates in people with type 2 diabetes with the general population.
The study included 137,804 individuals with median follow-up of 8.4 years. The authors found all-cause mortality rates decreased at all ages during the study period, likely owing to successful cardiovascular prevention and treatment, which means people live longer now and have a greater chance of experiencing other conditions. However, they note, diabetes screening, better management of diabetes and its complications, earlier cancer detection and improved cancer treatments seem to have benefited younger people with type 2 diabetes.
There were also higher “annual average percentage changes” (AAPC- the average percentage increase/decrease per year) in cancer mortality in women (1.5%) compared with men (1.0%), and higher cancer mortality AAPC for people with morbid obesity (5.8%) versus those in other weight categories (all below 1.0%). The gap in cancer mortality between smokers and non-smokers also increased and these authors suggest current healthcare policies and structures could benefit never-smokers more than smokers.
Constant upward trends in mortality rates were also observed for pancreatic, liver, and lung cancer at all ages, colorectal cancer at most ages, breast cancer at younger ages, and prostate and endometrial cancer at older ages.