Prostate Cancer Plus - Diabetes
Pre-Existing Diabetes Raises Cancer Patients' Risks
By Monday, December 15 2008 18:56
People with diabetes at the time of a cancer diagnosis have an increased risk of death compared to patients without diabetes, according to a study led by Frederick Brancati, M.D., Johns Hopkins University and published in the December 17 issue of The Journal of the American Medical Association today.
Having diabetes when receiving a cancer diagnosis increases the risk of death from any cause by 41% compared with the situation of newly diagnosed cancer patients without diabetes. This may be important for people with diabetes who are considering diagnostic tests and treatment choices.
For men with diabetes diagnosed subsequently with prostate cancer and for diabetics of either sex who develop lung, liver, gastric or pancreatic cancer, not enough evidence exists to conclude that diabetes heightens risks of death due to the cancer itself. But this might be because not enough research has been done.
According to one of the study's authors, Bethany B. Barone, Sc.M., of the Johns Hopkins Bloomberg School of Public Health, Baltimore, "the association of preexisting diabetes in newly diagnosed cancer patients with long-term, all-cause mortality has not been systematically assessed. Cancer patients with diabetes may receive less aggressive cancer treatment or less aggressive diabetes care, both of which could compromise survival."
Twenty million Americans now have diabetes mellitus, or about 7 percent of the U.S. adult population. Today more people develop diabetes before or during middle-age. Some of them are likely to develop a cancer also as they age and may even be more vulnerable some types of cancer. Diabetes mellitus does appears to be a risk factor for some cancers, Bethany Barone says. This study was necessary, she adds, because the effect of pre-existing diabetes on survival chances of newly diagnosed cancer patients is less clear. Background information from an American Cancer Society study and a UK National Health study showed conflicting results on whether cancer patients who already had diabetes were more likely to die than those without diabetes.
Specifically, Brancati, Barone and team write, "some cancers -- including cancers of the breast, colorectum, endometrium, liver, and pancreas -- occur more commonly in individuals with diabetes." Estimates of how much more prevalent diabetes is among newly diagnosed cancer patients than in the general population range "from 8% to 18%."
To find out more from, this team ran a broad literature search yielding nearly 8 thousand studies, winnowing these by stages to 94 studies with relevance to a systematic review. Then they reduced the number to 23 studies which were relevant and sufficiently well-designed and conducted with respect to evidence and verifiability. From this focused group of studies it emerged that pre-existing diabetes was significantly associated with increased long-term, all-cause death for cancers of the endometrium, breast, and colorectum. Diabetes was associated with a nonsignificant increase in risk in prostate, gastric, liver, lung and pancreatic cancer.
One effect of the winnowing process, though, was to reveal how few reliable studies have been done on this topic and how unevenly research plays out over the range of cancers. From the results of the selection process it looks as though cancers for which significant association between diabetes and "long-term, all cause death" were found happen to be cancers which attract more (and more rigorous) research. For example:
- The finding of "significant" increased risk of death from any cause for diabetes patients who develop breast, endometrial or colorectal cancer is based on 3 studies each for breast and endometrium and 4 for colon or colorectal cancer.
- By contrast, the finding of "nonsignificant" increase in similar risk for diabetes patients who develop pancreatic, liver or prostate cancer is based on just 1 study each for those cancer types.
If more good research has been done, actually, on diabetes and breast cancer than on diabetes and pancreatic, liver and also gastric cancer, does this reflect medical-scientific priorities or the results of massive funding of breast cancer research compared with funding of research into other cancers?
To put it another way -- if more, reliable research were to be done on prostate and lung cancer, the two commonest cancers in men, would it become as clear as it appears to be for breast and endometrial in women and colorectal cancer in both sexes that pre-exisiting diabetes does raise the overall risk of death?
Or in fact are prostate and lung cancer less associated with diabetes? This present study was completed too soon, apparently, to take note of the study published in October 2008 by Department of Nutrition, Harvard School of Public Health based on Health Professionals Follow-Up Study from 1986 to 2004, which found that "diabetes is associated with reduced prostate cancer risk."
The take-away message should probably fall on the cautionary side. Not enough evidence to reach statistical significance indicates that more studies are needed. The single study that Dr. Brancati and BAthany Barone's team accepted from prostate research, by a team at Schiffler Cancer Center, Wheeling, West Virginia led by Dr. Gregory Merrick in 2007, found that " Patient age, diabetes, and tobacco were the strongest predictors foroverall survival."
"Future research should determine the relative importance of different pathways to diabetes-related mortality risk," Barone's study concludes. "If a clinical or biological interaction between diabetes and cancer care is confirmed, subsequent trials should test whether improvements in diabetes care for patients with newly diagnosed cancer might reduce long-term mortality."
Long-term All-Cause Mortality in Cancer Patients With Preexisting Diabetes Mellitus: A Systematic Review and Meta-analysis.
Bethany B. Barone, ScM, Hsin-Chieh Yeh, PhD., Claire F. Snyder, PhD, Kimberly S. Peairs, MD. Kelly B. Stein, MD. Rachel L. Derr, MD, Antonio C. Wolff, MD, Frederick L. Brancati, MD, MHS. (JAMA. 2008;300[23]:2754-2764.)
