Researchers investigate diabetes effects on cancer mortality

Health conditions are often more than the sum of their parts, with different diseases often interacting in various ways. Type 2 diabetes is one example of a disease that is both serious on its own and linked to other conditions such as cardiovascular disease, cerebrovascular disease and various types of cancer. One such cancer type, colorectal cancer, is a leading cause of death among adults over 65 in the United States, and studies have found that up to 25 percent of colorectal cancer patients also have diabetes. However, little research has focused on how type 2 diabetes influences colorectal cancer death risk.

In a new study published in the International Journal of Colorectal Disease, researchers attempted to improve our understanding about how these two prevalent and serious health conditions are linked. The study was led by Sanae El Ibrahimi, PhD, MPH, at the University of Nevada, Las Vegas, in collaboration with Matthew Lee Smith, PhD, MPH, co-director of the Texas A&M Center for Population Health and Aging and associate professor in the Department of Environmental and Occupational Health at the Texas A&M School of Public Health, and a fellow researcher from the University of Miami. They investigated whether type 2 diabetes is a predictor of mortality from all causes and from colorectal cancer among older adults and how type 2 diabetes complications affect colorectal cancer survival rates.

Smith and colleagues analyzed data of colorectal cancer patients over the age of 67 from the National Cancer Institute from 2002 to 2011. These datasets cover approximately 28 percent of the U.S. population and contain information about demographic factors such as age, sex and race and clinical factors such as source of cancer diagnosis, date of diagnosis and survival in months. They also obtained data about type 2 diabetes status using inpatient and outpatient records from the Centers for Medicare and Medicaid Services for the same period. Their analyses covered more than 90,000 colorectal cancer patients with a mean age of 78, of whom 24 percent had been diagnosed with type 2 diabetes prior to their cancer diagnoses.

By the end of the study period, nearly half of the subjects had died, with more than half of those deaths due to colorectal cancer. Around 20 percent of the deceased subjects had type 2 diabetes, with 5 percent having complications. Their analyses found that colorectal cancer patients with type 2 diabetes and diabetes-related complications had an almost 50 percent higher risk of dying from any cause and 16 percent higher risk of death from colorectal cancer. These results are consistent with previous work finding links between diabetes and all-cause mortality.

Although Smith and colleagues found a significant association between type 2 diabetes and colorectal cancer deaths, the specific reasons for this relationship remains unknown.

“Factors related to type 2 diabetes such as hyperglycemia have been shown to increase cancer risk, and diabetes may affect the risk of colorectal cancer recurrence,” El Ibrahimi said. “Indirect influences may also play an important role such as diabetes status affecting treatment choices and the responses and side effects of some cancer treatments.”

This study highlights the importance of better managing diabetes through lifestyle changes, education and regular testing. Smith and colleagues also note that colorectal cancer patients with type 2 diabetes would likely benefit from disease self-management education programs. Further research is needed to fully study the links between diabetes and colorectal cancer mortality, with a focus on lifestyle behaviors and patient characteristics and more data on diabetes duration and cases of prediabetes.

“The findings of this study serve as a starting point for further exploring how type 2 diabetes and colorectal cancer interact, which is important because of the increasing prevalence of diabetes among older adults,” Smith said. “It also shows the importance of self-management and control of type 2 diabetes and possible avenues for health care professionals to help patients with colorectal cancer and type 2 diabetes improve their survival rates.”