According to recent estimates, colorectal cancer (CRC) ranks as the fourth most common cancer in the United States and the second most lethal. Colonoscopy screening has been considered the gold standard for CRC screening because it enables clinicians to view the entire colon and to detect and remove polyps during the same procedure to reduce subsequent risks of CRC. Despite the effectiveness of CRC screening, the American Cancer Society projects that more than 50,000 people in the U.S. die annually from the disease.

“Beyond the established risk factors for CRC like advanced age, smoking, and a familial history of the disease, recent studies have suggested that people with diabetes have a higher risk of developing CRC when compared to those without the disease,” says Joshua D. Miller, MD. Studies have been conducted to address the association between diabetes and adenoma detection rate (ADR) but results from these clinical trials have been mixed. “We need a better understanding of the role of type 2 diabetes in colorectal adenoma-carcinoma progression since diabetes affects nearly 10% of the U.S. population, or over 33 million Americans,” adds Dr. Miller.

A New Analysis

For a study published in Scientific Reports, Dr. Miller and colleagues conducted a retrospective review of initial screening colonoscopies while attempting to control for confounding variables. In addition, the authors analyzed the effect of anti-diabetes medications and glycemic control as measured by fasting plasma glucose (FPG) on the day of the colonoscopy and within 12 months of the procedure. Of the 2,865 screening colonoscopies assessed in the study population, 282 were performed on patients who had type 2 diabetes. Of these, 9.8% had type 2 diabetes while 2.4% had type 1 diabetes. Patients with diabetes were often treated with more than one medication.

“Our data showed that patients with diabetes had a significantly higher prevalence of adenomas and advanced adenomas than those without it,” Dr. Miller says. In a multivariable analysis, the study demonstrated that type 2 diabetes was associated with an increased ADR (odds ratio, 1.49), along with other factors, including smoking, older age, higher BMI, and male sex (Table). Type 2 diabetes was not significantly associated with advanced ADR after taking multiple confounding variables into consideration. However, other factors were significantly associated with an increased advanced ADR, including older age, male sex, smoking and increased BMI. For patients with type 2 diabetes, those not taking diabetes medications were more likely to have an adenoma than those taking these therapies (odds ratio, 2.38).

Assessing Implications

Results from the study suggest that type 2 diabetes is significantly associated with an increased risk of detecting at least one adenoma. In addition, two potentially modifiable variables were detected in increased BMI and smoking, both of which were significantly associated with increased ADR and advanced ADR.

“Early interventions for preventing type 2 diabetes, attention to glycemic control, and prescribing medications that treat the disease and its secondary complications may reduce risks for developing colonic adenomas,” says Dr. Miller. “Such efforts may also contribute to better CRC prevention. Clinicians should be aware of the association between diabetes and colorectal adenomas and perhaps recommend more frequent CRC screening in appropriate patients with diabetes. We should seize every opportunity to encourage patients to make lifestyle changes that can help reduce their risks for both CRC and diabetes.”

Of note, Dr. Miller and colleagues are conducting a prospective study in which patients with diabetes who are undergoing an initial screening colonoscopy will have their fasting insulin, C-peptide, and A1C levels measured prior to the procedure. “Our goal is to collect data on the biochemical components of diabetes and CRC,” says Dr. Miller. “We hope to establish the extent to which insulin resistance and/or hyperinsulinemia or other factors contribute to the increased risk of developing adenomas in a diverse patient group. This information may provide data on the specific pathways of diabetes and CRC progression and potentially help inform treatment decisions in the future.”