Type 2 diabetes associated with higher risk for developing colorectal cancer

Key takeaways:

• Patients who did not undergo colonoscopy screening and those with a smoking history have an elevated risk for colorectal cancer.
• Preventive screening can dramatically improve survival outcomes.

Risk for developing colorectal cancer increased by 47% among individuals with type 2 diabetes, according to results from a cohort study designed to over-represent African Americans and low-income patients.

The increased risk for colorectal cancer (CRS) may be reduced by colonoscopy screening among individuals with diabetes, according to researchers.

The findings — published in JAMA Network Open — suggest that diabetes prevention and control may potentially reduce colorectal cancer (CRC) disparities.

“In a cohort composed primarily of participants who self-report African American identity and low-income, diabetes diagnosis is consistently associated with increased risk [for] [colorectal cancer (CRC)],” Thomas Lawler, PhD, research assistant at University of Wisconsin-Madison, and researchers wrote. “Associations are greatest for the subgroups of participants with recent diabetes diagnosis and those without recent colonoscopy, highlighting the importance of [colorectal cancer] screening as a potential disruptor of the adverse outcomes of metabolic dysregulation to increase [colorectal cancer].”

Background and methodology

Although type 2 diabetes and colorectal cancer (CRC) disproportionately affect individuals with low socioeconomic status and who identify as African American, potential associations between diabetes and CRC have been understudied in these two populations.

Researchers conducted a cohort study representing understudied populations to determine if diabetes is associated with increased risk for CRC.

Researchers utilized data from the prospective Southern Community Cohort Study in the United States, which recruited participants from 2002 to 2009 to complete three follow-up surveys by 2018.

Of the approximately 85,000 participants (86% enrolled at community health centers; 14% enrolled via mail or telephone), researchers deemed 54,597 individuals (64% women, 66% African American, 53% with income less than than $15,000/year) as eligible due to the criteria of having more than 2 years of follow-up, no prior cancer diagnosis (other than nonmelanoma skin cancer) at enrollment, enrollment diabetes status listed and diagnosis of diabetes at age 30 years or later.

Results included physician-diagnosed diabetes and age at diagnosis via survey at enrollment and three follow-up evaluations.

Results, next steps

In total, 289 of the 25,992 study participants with diabetes developed CRC, whereas 197 of the 28,605 study participants without diabetes developed CRC; therefore, diabetes appeared associated with increased CRC risk (HR = 1.47; 95% CI, 1.21-1.79).

The analysis showed greater risk among individuals without colonoscopy screening (HR = 2.07; 95% CI, 1.16-3.67) and those with a smoking history (HR = 1.62; 95% CI, 1.14-2.31) — potentially due to cancer screening differences — as well as among participants with recent diabetes diagnoses (diabetes duration less than 5 years compared with 5 to 10 years; HR = 2.55; 95% CI, 1.77-3.67), possibly due to recent screening.

Researchers acknowledged several study limitations, including relying on self-reported diabetes diagnosis over medical records or blood testing, as well as the study including a majority of individuals with low socioeconomic status, which comes with a greater risk for undiagnosed diabetes prior to study enrollment.

The findings highlight the importance of preventive screenings and collaboration within the health care community to mitigate risk of developing CRS among those with diabetes, researchers explained.

“These findings contribute evidence of an association between diabetes and CRC risk,” researchers wrote.

“These associations were greatest for those with recent diabetes and those who did not participate in colonoscopy,” they added. “Increased interactions with the health care system following a diabetes diagnosis, including increased referrals to CRC screening, may be important for mitigating the harm of diabetes-related metabolic dysfunction, particularly in early diabetes, on CRC risk.”

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