Study shows CRC risk higher in people with insulin-requiring type 2 diabetes

A study published today in the American Gastroenterological Association’s journal Gastroenterology concludes that patients with type 2 diabetes mellitus who require long-term insulin therapy are at a significantly increased risk for colorectal cancer.

Results of this retrospective cohort study, conducted on 24,918 people with type 2 diabetes, suggest that those who received more than three years of insulin therapy during the follow-up period of the study have more than three times the risk of developing colorectal cancer than those who did not receive insulin therapy.

The prevalence of type 2 diabetes is at epidemic proportions and many patients will eventually require insulin therapy to manage their disease. “It is yet to be determined whether the increased risk of colorectal cancer is due to a growth promotional effect of exogenous insulin, the severity of type 2 diabetes mellitus, or both,” said Dr. Yu-Xiao Yang, lead study author. “However, we are hopeful that the identification of this group of patients at a significantly higher risk of developing colorectal cancer will lead to more effective cancer prevention efforts.”

Patients should not discontinue insulin therapy as a result of this study, but should ask their doctors about the highly effective colorectal cancer screening methods currently available. If confirmed in additional studies, practicing physicians should consider long-term insulin therapy as a marker of elevated colorectal cancer risk.

Further studies are needed to determine whether a more stringent colorectal cancer screening program is needed in this population. “At this point, we advocate for strict adherence to the existing colorectal cancer screening guidelines in this patient population, as these measures can effectively reduce the risk of developing colorectal cancer,” added Yang.

Colorectal cancer is the second leading cause of cancer-related death in the United States. Type 2 diabetes is a condition where the body responds poorly to the insulin that it produces, and has to make an excessive amount of insulin to overcome the poor response in order to maintain blood sugar control. At advanced stages, the body produces less and less insulin, until eventually insulin treatment is needed. Approximately 18 million Americans have diabetes–90 to 95 percent of these cases are type 2 diabetes.

Previous studies have suggested that type 2 diabetes mellitus may be independently associated with increased colorectal cancer risk. Excess internal insulin production in type 2 diabetes has been proposed as the main potential reason. However, the effect of externally administered insulin on cancer risk has not been studied in humans.

The American Gastroenterological Association (AGA) and multiple government agencies and professional societies underscore the importance of colorectal cancer screening for all individuals 50 years of age and older. Currently, there are a number of approved tests that may be used to screen for colorectal cancer, including barium enema, fecal occult blood test, flexible sigmoidoscopy and colonoscopy.

About the Study

Lead study author Dr. Yu-Xiao Yang is an instructor of medicine in the University of Pennsylvania School of Medicine’s division of gastroenterology. Researchers conducted a retrospective cohort study among all patients with a diagnosis of type 2 diabetes in the General Practice Research Database, a collection of primary outpatient medical records for hundreds of general practitioner practices in the United Kingdom. Patient information in the database includes demographic information, prescription drugs, diagnoses, hospital admissions and deaths. Of the 24,918 patients with type 2 diabetes, 3,160 required insulin. Results of the study are generalized and can be applied to various national populations.