Consensus statement reviews emerging evidence linking diabetes, cancer

A new consensus statement by experts assembled by the American Diabetes Association and American Cancer Society reviews emerging evidence that suggests cancer incidence is associated with diabetes, certain diabetes risk factors and treatments.

The statement, published in CA: A Cancer Journal for Clinicians, reviews the current evidence and science surrounding the association between diabetes and cancer incidence/prognosis; risk factors common to both diabetes and cancer; possible biologic links between diabetes and cancer risk; and whether diabetes treatments influence the risk for cancer or cancer prognosis.

Recent evidence from observational studies suggests that some medications used to treat hyperglycemia, such as insulin glargine, are associated with an increased risk for cancer, and others, such as metformin, are associated with a reduced risk for cancer.

“Traditionally, there hasn’t been much overlap between research in cancer and in diabetes,” Edward Giovannucci, MD, co-chair of the consensus report group, said in a press release. “But recently it has become clearer that there are fascinating links between the two.”

Review of evidence, science

The American Diabetes Association (ADA) and American Cancer Society (ACS) convened a consensus development conference in December 2009. There, experts addressed current gaps in evidence, potential research and epidemiological strategies for developing more definitive evidence in the future.

The consensus group concluded that diabetes — primarily type 2 diabetes — is associated with an increased risk for some cancers, including those of the liver, pancreas, endometrium, colon/rectum, breast and bladder, and a reduced risk for prostate cancer. For other cancer sites, there appears to be no association or evidence is inconclusive.

Based on available evidence, 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. Further, the group concluded that possible mechanisms for a direct link between diabetes and cancer include hyperinsulinemia, hyperglycemia and inflammation.

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.

Limited, early evidence suggests that metformin is associated with a lower risk for cancer and exogenous insulin is associated with an increased risk for cancer. However, further research is needed to clarify these issues and evaluate the possible association of insulin and other diabetes medications with the risk for cancer, according to the report.

Other findings and recommendations include:

• Healthy diet, physical activity and weight management reduce the risk and improve outcomes of type 2 diabetes and some forms of cancer, and should be promoted for all.
• Patients with diabetes should be strongly encouraged by their health care professionals to undergo appropriate cancer screenings as recommended for all people of their age and sex.
• Cancer risk should not be a major factor when choosing between available diabetes therapies for the average patient. For selected patients with a very high risk for cancer occurrence (or for recurrence of specific cancer types), these issues may require more careful consideration.

Many questions remain

“Our summary may raise more questions than provide answers, but we hope that it will spur additional studies,” Giovannucci said.

Regardless, the majority of patients with diabetes do not need to consider the risk for cancer when deciding on diabetes therapy.

“Only patients with a very high risk for cancer occurrence, or re-occurrence, may wish to carefully consider their options,” David M. Harlan, MD, co-chair of the consensus report group, said in a press release. “Even then, the association appears to exist for some cancer types, and not for others. We have much to learn.” – by Katie Kalvaitis

From both the perspective of the ADA and ACS, we felt that the myriad information on diabetes and cancer risk that was out there had come in bits and pieces and, in a sense, each one was in very different context. The hope was that by gathering this group of experts and asking them to provide a unified report it would directly address, based on ‘best available evidence,’ what questions we can answer at this point and what questions we cannot answer. All of the observations that have been reported to date raise specific questions about whether diabetes itself increases cancer risk, whether some characteristic of diabetes and obesity raises cancer risk or whether the cumulative effects of both are true. We hope this report allows people to focus on specific research questions. While all existing therapeutic classes were examined, there is limited and still very early evidence as to the benefit and risk for these classes of therapies. Cancer risk should not be a major factor when choosing between available diabetes therapies. This is a critical piece of the consensus report. While many research questions remain, this report can help us prioritize those research questions more effectively.

– David M. Kendall, MD
Chief Scientific & Medical Officer for the American Diabetes Association

Giovannucci E. CA Cancer J Clin. 2010;doi;10.3322/caac.20078.

Follow HemOncToday.com on Twitter.