Older women with diabetes face more than double the risk for some types of colorectal cancer.

Colorectal cancer is the third leading cause of cancer deaths among women in the United States. Diabetes has been identified as a colon cancer risk factor, but the mechanisms are not completely understood. Researchers examined data from 37,695 participants of the Iowa Women’s Health Study (IWHS), which enrolled women over age 55 in 1986 and remains ongoing. Of these women, 2,361 reported a diagnosis of type 2 diabetes and 1,200 developed colorectal cancer.

The researchers obtained tumor tissue samples from IWHS participants who were diagnosed with colorectal cancer. They linked the tissue samples with other IWHS data, looking for cancer pathways and risk factors, and whether those risk factors were associated with three different molecular markers: microsatellite instability (MSI), CpG island methylation (CIMP), and BRAF gene mutations.

“Diabetes was more strongly associated with the MSI-high, CIMP-positive and BRAF-mutation cancer subtypes in this group of older women,” Mayo Clinic gastroenterologist Paul Limburg, M.D., was quoted as saying. Dr. Limburg explained that diabetes appeared to confer a greater than twofold increase in risk for these molecularly defined tumors.

“Knowing that diabetic women have these findings should help to facilitate more appropriate colorectal cancer prevention and treatment options,” study presenter Anthony Razzak, M.D., a Mayo Clinic research fellow, was quoted as saying. “Our findings may lead to new strategies for colon cancer screening, chemotherapy and chemoprevention in women with diabetes.”

SOURCE: Presented at the annual meeting of the American Gastroenterological Association, New Orleans, May 2, 2010