Lower risk for prostate cancer seen among antidiabetic drug users

The odds ratio for the risk for prostate cancer was 16% lower among men using antidiabetic drugs, according to recently published data.

Using the Finnish Cancer Registry, researchers from the University of Tampre and the Finnish Cancer Institute in Finland identified incident prostate cancer cases that occurred between 1995 and 2002.

The researchers matched each case with a control using the Population Register Center; 24,723 case-controlled pairs were included. Median age for both groups was 68 years.

Based on data from a prescription database, the researchers found that glibenclamide (5.1% of cases and 5.8% of controls), metformin (3.9% of cases and 4.6% of controls) and human insulin (2.4% and 3%) were the most commonly used drugs among both groups.

Ever use of antidiabetic drugs — including metformin, glibenclamide, glipizide and human insulin — was associated with a decreased risk for prostate cancer (OR=0.87). The amount of oral drugs and insulin used decreased the overall risk for prostate cancer (P_trend<.001 and P_trend=.009), but the risk for advanced disease was not dose dependent. However, the researchers reported that risk estimates for advanced disease were below 1 for all, except for patients using the smallest amount (,228 defined daily dose) of oral drugs.

Men with seven years of antidiabetic drug treatment prior to diagnosis/reference had an overall risk for prostate cancer that was 34% lower than for men not using any antidiabetic medication (P_trend<.001). The risk for advanced disease in seven-year users was 39% lower (P_trend=.003). – by Stacey L. Adams

Am J Epidemiol. 2008;168:925-931.

The problem is that the researchers don't know exactly why it is that this prostate cancer risk is reduced. At this point they don't really have the evidence to prove that it's the drug and they believe that it may be more about the diabetes condition that may offer this type of unfortunate protection. If you're diabetic, then you have a little protection, but diabetes is not something you want to have. The jury is still out, and they need to close the gap on understanding this relationship of having diabetes and reduced risk for prostate cancer.

One of the issues of diabetes is insulin resistance in tissues. Many times cancer cells respond favorably to insulin; it helps them grow, but it may be the diabetic condition that fosters this, not just insulin resistance to tissues. But diabetes may offer that resistance to the tumor cell itself and thus doesn't allow for that growth to occur. To suggest that that is the actual mechanism of it is absolute speculation. But it is kind of interesting and intriguing that all of the oral drugs — the antidiabetic drugs — seem to have a favorable effect. The researchers state that the decrease in cancer risk was seen with most drug groups. These drugs have different types of effects in terms of trying to improve glucose metabolism. Some may help to increase insulin output from the pancreas and others may help sensitize muscle or insulin-sensitive tissues to insulin, which are very different actions. However, the researchers found that these drugs, virtually all of them, are related to a decrease in prostate cancer, which makes the claim that these drugs lower risk a curious relationship without understanding the cause.

The obese condition of individuals may also be of interest. There may be a number of emerging unfortunate lifestyle conditions that play out in aiding or preventing this type of cancer to occur in men. There are a lot of areas that are, unfortunately, not able to be addressed in this study, so the researchers are going to have to move forward and get more information, particularly with regard to serially measured PSA levels.

– Larry S. Verity, PhD, FACM

Professor of Exercise Physiology, Department of Exercise and Nutritional Sciences,

San Diego State University