A joint consensus statement from the American Diabetes Association and the American Cancer Society released June 16 reviews the current state of science regarding the complex relationship between diabetes and cancer.
Epidemiologic evidence suggests that people with diabetes—type 2 in particular—are at increased risk for cancer. The reasons for this association are poorly understood, but there is evidence to support roles for risk factors that are common to both disorders and medications used to treat diabetes, as well as possible direct causal links.
The American Diabetes Association and the American Cancer Society convened a consensus development conference to examine these associations in December 2009. The writing group independently developed a statement that solely represents the positions of the nine panel members and does not reflect official positions of either sponsoring organization (Diabetes Care 2010;33:1674-85).
The panel, which was chaired by Dr. Edward Giovannucci of the Harvard School of Public Health, Boston, recommended that health care professionals strongly advise patients with diabetes to undergo appropriate cancer screenings as advised for all people in their age and sex categories. Promotion of healthful diets, physical activity, and weight management is encouraged for all patients to reduce risk and improve outcomes of type 2 diabetes and some forms of cancer.
The statement also recommended that cancer risk not be a major factor in choosing between available diabetes therapies for the average patient, but that for selected patients at very high risk for cancer occurrence—or for recurrence of specific cancer types—these issues may require more careful consideration.
The statement was organized around answers to four basic questions:
▸ Is there a meaningful association between diabetes and cancer incidence or prognosis? Cancer and diabetes are diagnosed within the same individual more frequently than would be expected by chance, even after adjustment for age. However, the association appears to be limited to certain types of cancer, while other cancers appear to be less common among people with diabetes. Specifically, type 2 diabetes is associated with an increased risk for cancers of the liver, pancreas, endometrium, colon/rectum, breast, and bladder, but with a reduced risk of prostate cancer. For some other cancer sites there appears to be no association or the evidence is inconclusive.
▸ What factors are common to both cancer and diabetes? The association between diabetes and some cancers may be due in part to shared risk factors between the two diseases, such as aging, obesity, diet, and physical inactivity. Smoking appears to be an independent risk factor for the development of diabetes and diabetes complications, in addition to cancer. Evidence for the role of alcohol is mixed. Even moderate alcohol consumption increases the risk for certain types of cancer and excess alcohol consumption is also a risk factor for diabetes. However, moderate alcohol consumption is linked with a reduced incidence of diabetes.
▸ What are the possible biologic links between diabetes and cancer risk? The document provides detailed summaries of the evidence pertaining to the potential roles of the insulin/insulin-like growth factor receptor axis, hyperglycemia, hyperinsulinemia, and inflammatory cytokines/inflammation.
▸ Do diabetes treatments influence cancer risk or cancer prognosis? The evidence for specific drugs affecting cancer risk is limited, and observed associations may have been confounded by indications for specific drugs, effects on other cancer risk factors such as body weight and hyperinsulinemia, and the complex progressive nature of hyperglycemia and pharmacotherapy in type 2 diabetes.
Although still limited, early evidence suggests that metformin is associated with a lower risk of cancer and that some exogenously administered insulin is associated with an increased cancer risk. Further research is needed to clarify these issues and evaluate if insulin glargine is more strongly associated with cancer risk, compared with other insulins.
The statement also highlights numerous remaining research questions.
The consensus development conference was supported by an unrestricted grant from Amylin Pharmaceuticals Inc., Lilly USA, Merck & Co. Inc., Novo Nordisk A/S, and Sanofi-Aventis. Five of the eight study authors reported financial ties with these and other pharmaceutical companies.
Diabetic patients should undergo cancer screenings as advised for all people in their age and sex categories.
Source DR. GIOVANNUCCI