Men with type 2 diabetes have a moderately higher risk of developing colorectal cancer than do men who are not diabetic, Peter T. Campbell, Ph.D., and his colleagues said in the October issue of Gastroenterology (doi: 10.1053/j.gastro.2010.06.072).
In contrast, type 2 diabetes shows no association with colorectal cancer risk among women. The reason for this gender discrepancy is unknown, said Dr. Campbell of the American Cancer Society’s epidemiology research program, and his coauthors.
Nevertheless, “these results emphasize the need for diligent adherence to recommended guidelines for colorectal cancer early detection among men with longstanding type 2 diabetes,” they noted.
A 2005 meta-analysis of epidemiologic studies found that type 2 diabetes moderately raised the risk of colorectal cancer in both sexes, but more recent analyses have consistently demonstrated a stronger association for men than for women. Given the high worldwide prevalence of diabetes and the significant morbidity and mortality associated with colorectal cancer, any link between the two diseases would have strong public health and clinical relevance, the investigators said.
They studied the relationship between diabetes and colorectal cancer using data from the Cancer Prevention Study II Nutrition Cohort. Participants were aged 50-74 years at baseline in 1992-93 and were followed through 2007.
In a sample of 73,312 men and 81,663 women from this cohort, 1,567 men and 1,242 women developed incident colon or rectal cancer. A total of 227 of these men and 108 of the women reported they had type 2 diabetes.
For men, diabetes was associated with a 24% higher risk of colorectal cancer. The link did not differ meaningfully by tumor stage or location within the colorectum. The risk was not markedly different between men who reported using insulin and those who did not.
The cancer risk increased with duration of diabetes. There was a null association with diabetes of up to 10 years duration, a relative risk of 1.35 for diabetes of 11-15 years duration, and a relative risk of 1.73 for diabetes of more than 15 years duration.
In contrast, among women there was no association between diabetes and colorectal cancer.
“These findings provide at least partial support for the hypothesis that hyperinsulinemia, hyperglycemia, or related cofactors are associated with higher colorectal cancer risk,” Dr. Campbell and his colleagues said.
They also suggest that the use of insulin probably doesn’t raise the risk of colorectal cancer substantially, the researchers added.
The reason for the difference in risk between men and women is not known, but it may be related to their differences in the degree of glucose control in recent years. National data suggest that women have better hemoglobin A1c levels than do men and are more apt to take metformin, both of which suggest that women have better glucose control.
The researchers also found a stronger association between diabetes and colorectal cancer among patients who reported a family history of colorectal cancer (RR 1.91) than among diabetics who had no family history of the cancer (RR 1.12). “To our knowledge, these are the first data to suggest that family history of colorectal cancer may modify the association between type 2 diabetes and colorectal cancer,” the team said.
This study was limited by its reliance on patient self-reports and the lack of pharmacologic data on diabetes therapy or degree of glucose control.
This study was supported by the American Cancer Society. No conflicts of interest were reported by the authors.