New research has found that cancer mortality in individuals with type 2 diabetes is substantially higher than the general population, according to a study published in Diabetologia.
The study found that cancer mortality rates among patients with type 2 diabetes were 18% higher for all cancers combined, 9% higher for breast cancer, and 2.4 times higher for colorectal cancer, compared to the general population. Cancer mortality in individuals with diabetes was also around double compared with the general population for diabetes-related cancers, such as liver, pancreatic, and endometrial cancers.
The study also noted increasing breast cancer mortality rates by 4.1% per year among younger women with type 2 diabetes across the 20-year study period from 1998 to 2018.
A growing body of epidemiological evidence has shown a higher risk of incidence and mortality for some types of cancer in patients with type 2 diabetes. The underlying biological mechanisms for this association include prolonged exposure to the effects of increased blood sugar and insulin levels, insulin resistance, and chronic inflammation. Robust evidence also suggests that there is a causal relationship between type 2 diabetes and pancreatic, liver, and endometrial cancers.
Although previous studies have extensively investigated inequalities in cardiovascular outcomes among people with type 2 diabetes, less is known about whether these inequalities exist in cancer mortality rates.
In the new study, investigators used a cohort of individuals aged 35 years or older who had newly diagnosed type 2 diabetes between January 1, 1998, and November 30, 2018. They 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 individuals with type 2 diabetes with the general population.
The study included 137,804 individuals with newly diagnosed type 2 diabetes with a median follow-up of 8.4 years. According to the study, all-cause mortality rates decreased at all ages between 1998 and 2018. Cancer mortality rates (all cancers combined except non-melanoma skin cancer) mortality rates also decreased for 55-year-olds by 1.4% per year and 65-year-olds by 0.2% per year but increased for 75-year-olds by 1.2% per year and 85-year-olds by 1.6% per year.
Constant upward trends in mortality rates were also observed for pancreatic, liver, and lung cancers at all ages; colorectal cancer at most ages; breast cancer at younger ages; and prostate and endometrial cancers at older ages.
Compared with the general population, individuals with type 2 diabetes had a more than 1.5-fold increased risk of colorectal, pancreatic, liver, and endometrial cancer mortality during the entire study period. Despite national reports showing a decrease in breast cancer mortality in the younger age ranges, the new research also showed increasing breast cancer mortality rates by 4.1% per year in the younger women with type 2 diabetes.
“From this perspective, our results suggest that it may be helpful to extend breast cancer screening to young women with type 2 diabetes,” the authors wrote. “However, given the high cost and potentially longer exposure to screening procedures, cost-effectiveness analyses are required to define the appropriate time window and identify subgroups who may benefit more.”
Decreasing cardiovascular mortality was observed in older age groups, which was attributed to successful cardiovascular prevention and treatment in recent decades. However, this means that individuals live longer and have a greater chance of developing or dying from other conditions, such as cancer. However, the investigators noted that diabetes screening and improved management, as well as earlier cancer detection and improved treatments, seem to have benefitted younger patients with type 2 diabetes in the same way as they have the general population.
The investigators also noted higher annual average percentage changes (AAPC) in cancer mortality among women (1.5%) compared with men (1%), although women had lower cancer mortality throughout the study period. Biological factors, health seeking behaviors, and lifestyle factors, such as smoking and obesity, all differ between men and women, although the relative contribution of each to cancer mortality is not known. The wealthiest population also had a higher AAPC (1.5%) than the poorest (1%), leading to a narrowing but persistent gap by socioeconomic status, according to the study authors.
Other key findings included higher cancer mortality AAPC for individuals with morbid obesity (5.8%) versus those in other weight categories (all <1%), as well as a higher cancer mortality AAPC for White patients (2.4%) compared with an average annual percentage fall of 3.4% across non-White ethnicity combined.
The gap in cancer mortality between smokers and non-smokers also increased, with patients who smoke seeing an increased cancer mortality AAPC of 3.4%, while the AAPC fell by 1.4% for non-smokers. The study authors suggest that current health care policies and structures could benefit those who have never smoked more than smokers, but tailored interventions for smokers could help address their increasing cancer mortality.
“The prevention of cardiovascular disease has been, and is still considered, a priority in people with diabetes,” the authors wrote. “Our results challenge this view by showing that cancer may have overtaken cardiovascular disease as a leading cause of death in people with type 2 diabetes. Cancer prevention strategies therefore deserve at least a similar level of attention as cardiovascular disease prevention, particularly in older people and for some cancers such as liver, colorectal, and pancreatic cancer.”