Diabetes Increases Colorectal Cancer Risk for Women

Dec. 7, 2007 — -- Women with diabetes already have to manage a complex diagnosis and treatment protocol. Now they may have another disconcerting diagnosis: colorectal cancer.

According to a study released Friday, women with diabetes are 1.5 times more likely to develop colorectal cancer -- in which cancerous tumors develop in the tissues of the colon or rectum -- than women who don't have the metabolic disorder.

The research was announced Friday at the American Association for Cancer Research's Sixth Annual International Conference on Frontiers in Cancer Prevention Research.

"We are just beginning to understand the role of insulin in the increased risk of many cancers," said Dr. Andrew Flood, the study's lead author and assistant professor of epidemiology and community health at the University of Minnesota School of Public Health.

"Our primary finding in this study was that a diagnosis of diabetes meant a 50 percent stronger chance of developing colorectal cancer."

Flood and his colleagues examined data from a large-scale cancer screening study known as the Breast Cancer Demonstration Project, which took place during the 1970s at 29 different medical facilities. They tracked the records of more than 45,000 female participants to identify how many women later developed colorectal cancer.

After adjusting for a number of variables, Flood said the results remained statistically significant, and he believes insulin has something to do with it.

"Elevated rates of insulin itself may promote the risk," he said.

Higher Insulin Means Higher Risk?

Dr. David Beck, chairman of the department of colon and rectal surgery at the Ochsner Clinic Foundation in New Orleans, agrees that insulin may play a role in cancer development.

"Insulin is important in cells' ability to use glucose, one of the cells' major energy source," he said. "Elevated glucose levels might support cell growth initially or may contribute to new blood vessel growth, which would allow cells to grow faster. This might be a factor in other cancer development."

To test the hypothesis that higher insulin levels -- common in people developing diabetes or people who have poorly managed glucose -- triggered cancerous polyps, Flood and his colleagues then examined other data from women who were later diagnosed with diabetes. They were surprised to find that women in this "prediabetic" stage did not actually have as high an increased risk.

"People who are prediabetic have higher levels of insulin, so we expected to see a greater risk," said Flood. "But that's not what we found."

The exact way reason that increased insulin hastens the development of cancer cells remains largely unknown. Flood suspects it may have something to do with the length of time and the degree of elevated insulin in the body.

Flood said that further study needs to be done to find statistics for diabetic men and development of colorectal cancer and to determine the the risk of developing other cancers. He points to pancreatic cancer as another possible illness that insulin can affect.

The best way women with diabetes can help their bodies not to develop colorectal cancer is through "management of glucose," according to Flood. "That's what they can do."

Beck reminds patients that colonoscopies that look for polyps are the first line of defense.

"Healthy lifestyles and diet are important, however colorectal cancer screening with colonoscopy is critical to the prevention of colorectal cancer," he said. "If diabetic women are at increased risk, it is even more important to screen them and we may consider decreasing the time for follow-up exams."

Concerns About Colorectal Cancer

Outside of skin cancers, colorectal cancer is the third most common cancer found in men and women in America. The American Cancer Society (ACS) estimates that there will be about 112,340 new cases of colon cancer and 41,420 new cases of rectal cancer in 2007 in the United States. Combined, they will cause about 52,180 deaths.

The death rate from colorectal cancer has been decreasing for the past 15 years, according to the ACS. One reason is that there are fewer cases. Thanks to colorectal cancer screening, polyps can be found and removed before they turn into cancer.

This most recent research may help reveal the mechanisms of colorectal cancer. "I think the study is interesting as it provides additional evidence of the many factors that encourage development and growth of colon polyps and tumors," said Beck. "It will stimulate additional research in this important area."