Long-term insulin use by patients with type 2 diabetes is associated with an increased risk of colon cancer, according to research reported in the medical journal Gastroenterology.

Dr. Yu-Xiao Yang and colleagues, based at the University of Pennsylvania School of Medicine in Philadelphia, conducted a study among patients in the General Practice Research Database from the UK. The researchers compared insulin use between 125 diabetic patients who developed colon cancer and 1195 similar diabetic subjects who did not.

The researchers estimate that if 100,000 insulin users were followed for 1 year, 197 would develop colon cancer. By contrast, if the same number of non-insulin users were followed, only 124 would develop colon cancer.

The risk of colon cancer seemed to rise as the duration of insulin use increased. For example, insulin use for 3 to 5 years raised the cancer risk by threefold, whereas use for more than 5 years increased the risk by about fivefold.

There was no evidence that other diabetes drugs, such as metformin or sulfonylurea, increased the risk of colon cancer.

Since diabetics can rarely substitute other drugs for their insulin, the researchers recommend that they strictly adhere to colon cancer screening guidelines.

SOURCE: Gastroenterology, October 2004.