Type 2 Diabetes Linked to Increased Risk of Colorectal Cancer

By Marilynn Larkin

June 15, 2020

NEW YORK (Reuters Health) - The increased risk of colorectal cancer associated with type 2 diabetes in people under age 50 is close in magnitude to the risk with a family history of the disease, according to a Swedish registry study.

Dr. Mahdi Fallah of the German Cancer Research Center (DKFZ) in Heidelberg told Reuters Health by email the findings are important so that for now, "risk-adapted colorectal cancer screening can be offered to diabetic patients earlier than the general population, or at least as soon as they become eligible for colorectal cancer mass screening."

"So far, we know that diabetic patients should be screened earlier, but we do not know exactly how many years earlier," he acknowledged. To investigate this further, he said, his team will use the same approach they described June 3 in Gastroenterology, which yielded starting ages for colorectal cancer screening based on family history. (https://bit.ly/2MORKSq)

Dr. Fallah and colleagues studied data from more than 12 million individuals born after 1931 and their parents, including 559,375 diabetic patients and 162,226 CRC patients.

As reported May 21 in the American Journal of Gastroenterology, a type 2 diabetes diagnosis before age 50 was associated with a 1.9-fold increased risk of CRC before age 50 versus a 1.3-fold risk of CRC at/after age 50.

A diagnosis before age 50 in those with a family history of CRC was associated with a 6.9-fold risk of CRC before age 50 and a 1.9-fold risk of CRC at/after age 50.

Further, diabetic patients had a similar lifetime risk of CRC before age 50 (0.4%) as those with only a family history (0.5%) - double that of the general population (0.2%).

Study co-leader Dr. Elham Kharazmi, also of DKFZ, said by email: "Researchers with valid information on diabetic patients (especially by diabetes type), family history of colorectal cancer, and colorectal cancer outcome are encouraged to investigate the mechanism behind the association we found. This may eventually lead to prevention of early-onset colorectal cancer, which is globally on the rise among young adults."

Dr. Trilokesh Kidambi, director of the Colon Cancer Screening Program at City of Hope in Duarte, California, commented in an email to Reuters Health, "There is little doubt that these results are valid, as many of the patients I see with early-onset colon cancer or large, precancerous polyps do have a history of diabetes and other features of the metabolic syndrome."

"The primary limitation of this study is that it was unable to delineate the direct effect of diabetes on colon cancer risk and to separate this from other components of the metabolic syndrome such as obesity and high cholesterol, which are associated with and can contribute to risk of diabetes development," he said. "In other words, diabetes may represent the end product of several metabolic factors that increase a patient's risk of developing colon cancer, as well as other well-known medical problems."

"Additionally, it is not clear if duration (i.e., the number of years the patient's body has been exposed to higher blood sugar levels and changes in insulin levels) or severity (how well controlled the blood sugar has been) of diabetes influences the risk of colon cancer, which is critical to apply this type of data to the patients we see in practice," he said.

"I would use this data as yet another reason to motivate my diabetic patients to try and control their disease through diet, exercise and medications, and if a diabetic patient came to my office with concerning gastrointestinal symptoms, I would have a lower threshold to perform a colonoscopy," Dr. Kidambi concluded.

SOURCE: https://bit.ly/2B2NhJ4 American Journal of Gastroenterology, online May 21, 2020.