Diabetes Doubles Risk of Colorectal Cancer in Some Women

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Older women who have diabetes face another potential health challenge: colorectal cancer. Researchers from Mayo Clinic report that having diabetes more than doubles the risk of developing certain types of colorectal cancer among women older than 55.

A link between colon cancer and diabetes, and colorectal cancer and metabolic syndrome has been noted in previous research. Metabolic syndrome is associated with an increased risk of diabetes and is characterized by insulin resistance and abdominal obesity.

The prevalence of both diabetes and metabolic syndrome is significant among women: the American Diabetes Association reports that 10.2 percent of women age 20 and older have diabetes, and that 23.1 percent of adults age 60 and older have the disease. The figures for metabolic syndrome are even greater: the American Heart Association notes that 32.6 percent of women have metabolic syndrome, and among those age 60 and older, the figure is 54.4 percent.

Now add colorectal cancer to the picture. This type of cancer is the third leading cause of cancer-related death among women in the United States. In 2009, the estimated number of new colon cancers diagnosed in women was 54,090, and for rectal cancer, the figure was 17,290, according to the American Cancer Society. The expected number of deaths due to colorectal cancer in women was 24,680.

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The researchers at Mayo Clinic evaluated data from 37,695 subjects who were part of the Iowa Women’s Health Study, which recruited women ages 55 and older beginning in 1986. From this group of women, 2,361 had been diagnosed with type 2 diabetes and 1,200 had developed colorectal cancer. The investigators then set out to uncover links between the two diseases.

Based on their evaluation of tissue samples from the women with colorectal cancer, they found that having diabetes was “more strongly associated” with the presence of three different molecular markers: microsatellite instability (MSI), CpG island methylation (CIMP), and BRAF gene mutations, according to Paul Limburg, MD, a gastroenterologist at Mayo Clinic.

“Strongly associated” translates into a more than twofold increase in risk for these specific molecularly-defined tumors in women with diabetes when compared with women who did not have diabetes. This finding “should help to facilitate more appropriate colorectal cancer prevention and treatment options,” notes Anthony Razzak, MD, a Mayo Clinic research fellow.

In another current study, published in Cancer Causes & Control, investigators evaluated data from 45,516 women enrolled in the BCDDP (Breast Cancer Detection Demonstration Project). Women who had diabetes had a significantly increased risk of colorectal cancer compared with women without diabetes. The researchers also observed that the risk of colorectal cancer was time dependent: women diagnosed with diabetes between 4 and 8 years previously had a more than double risk of cancer compared with those diagnosed less than 4 years prior.

The Mayo Clinic findings, which are being presented during Digestive Disease Week 2010, the annual meeting of the American Gastroenterological Association, highlight the importance of screening older women with diabetes for colorectal cancer. “Our findings may lead to new strategies for colon cancer screening, chemotherapy and chemoprevention in women with diabetes,” said Dr. Razzak.

SOURCES:
American Cancer Society
American Diabetes Association
American Heart Association
Flood A et al. Cancer Causes & Control 2010 Apr. 10
Mayo Clinic
Pais R et al. World Journal of Gastroenterology 2009 Nov 7; 15(4): 5141-48

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