Diabetes linked to increased risk of colorectal cancer: JAMA

"Our finding that shorter diabetes duration is associated with elevated risk of colorectal cancer may be partially attributable to increased interactions with the healthcare system after diabetes diagnosis, allowing for opportunities for cancer screening," researchers wrote.

Type 2 diabetes and colorectal cancer disproportionately burden individuals of African American race and low socioeconomic status. Diabetes is an emerging risk factor for CRC, however, associations between diabetes and CRC have not been studied well in these populations. To fill this knowledge gap, Thomas Lawler, University of Wisconsin Carbone Cancer Center, Madison, and colleagues aimed to determine if diabetes is associated with the risk of colorectal cancer in a cohort representing understudied populations in a cohort study.

For this purpose, the researchers used data from the prospective Southern Community Cohort Study in the US, which recruited from 2002 and 2009 and completed three follow-up surveys by 2018. Of about 85,000 participants, 14% enrolled via mail or telephone, while 86% were enrolled at community health centres from the same 12 recruitment states.

They excluded participants with less than 2 years of follow-up, missing enrollment diabetes status, previous cancer diagnosis at enrollment, diabetes diagnosis before 30, and without diabetes at enrollment with no follow-up participation.

Diabetes diagnosis was hypothesized to be positively associated with the risk of CRC before analysis. Incident CRC was evaluated via National Death Index linkage and state cancer registry. Using time-varying diabetes exposure, hazard ratios were obtained via Cox proportional hazard models.

The study revealed the following findings:

• Among 54 597 participants, the median enrollment age was 51 years, 64% were female, and had income less than $ 15,000 per year.
• In total, 289 of 25 992 participants with diabetes developed CRC, vs 197 of 28 605 participants without diabetes.
• Diabetes was associated with an increased risk of colorectal cancer (hazard ratio [HR], 1.47).
• Greater associations were observed among participants without colonoscopy screening (HR, 2.07) and with smoking history (HR, 1.62), potentially due to cancer screening differences.
• Greater associations were also seen for participants with recent diabetes diagnoses (diabetes duration <5 years compared with 5-10 years; HR, 2.55), possibly due to recent screening.

"The results contribute evidence of an association between diabetes and CRC risk," the researchers wrote. "These associations were greatest for patients with recent diabetes, and who did not participate in colonoscopy."

They suggest the importance of increased interaction with the health care system following a diagnosis of diabetes, including increased referrals to CRC screening for mitigating the harm of diabetes-related metabolic dysfunction, particularly in early diabetes, on CRC risk.

Reference:

Lawler T, Walts ZL, Steinwandel M, et al. Type 2 Diabetes and Colorectal Cancer Risk. JAMA Netw Open. 2023;6(11):e2343333. doi:10.1001/jamanetworkopen.2023.43333.