Statins and Prostate Cancer

The Wall Street Journal is reporting on a study published in the journal Cancer, and described by Reuters that links statins to reducing the risk of prostate cancer.  According to the report:

The researchers found that men who died of prostate cancer were half as likely to have taken a statin at any time, and for any duration, than men in the "control" group.  Those with fatal cancers were 63 percent less likely to have ever taken a statin, according to findings published in Cancer.

 I would love for statins to reduce the risk of prostate cancer. Readers of this blog know I am relatively pro-statin, in the right patient population. However, this study is too limited to make an actual connection, and I would not recommend taking statins solely for prostate cancer prevention.

What did the researchers do? The looked at the medical records of 380 men who died of prostate cancer and matched them with the records of another 380 men who did not have prostate cancer.  They use statistical techniques to adjust for difference such as age, weight and other medications.

What's the problem with the study? First, if the study findings are correct, such a study that uses medical  records and then looks back in time can not prove causation.  It only proves association.  This means that the study doesn't prove that taking a statin will ward off prostate cancer. Rather, the results mean that men who had died of prostate cancer were less likely to take a statin.  This is a big difference.  There are multiple examples where a confirmed association did not result into a confirmed causation (Vitamin E/C and  Folic Acid for preventing heart attacks).  In addition, there are many reasons that the association is in fact not correct.  Perhaps men who had been diagnosed with prostate cancer chose not to take statins, even if their doctors recommended it, because they were more concerned about the prostate cancer?  Perhaps men who did not have prostate cancer were extremely health conscious and were more aggressive about both doing things to prevent cancer (exercise, diet, etc.) as well as being more aggressive about  taking statin medications for high cholesterol?

Why this might be true? The only way to truly determine causation is to perform a randomized clinical trial (RCT).  Only a RCT can both eliminate some of the confounding variables (i.e. were the men without prostate cancer more aggressive about their overall health) and demonstrate the primary ingredient for causation: that exposure always precedes the outcome.  If factor "A" is believed to cause a disease,  then it is clear that factor "A" must necessarily always precede the occurrence of the disease. 

However, there are two findings from this study that support causation.  First, is dose-response relationship.  Only the newer, more potent statins showed benefit. Taking a lower potency statin was not protective.  The second is biologic plausibility. According to the Reuters report, Dr. Stephen Freedland, who studies prostate cancer at the Duke University Medical Center in Durham, but wasn't involved in the new study was quoted as stating that statins may protect against fatal prostate cancer through their known cholesterol-lowering effects, mentioning that cholesterol is a "key nutrient" for cancer cells, so lower cholesterol levels in the body could prevent more aggressive forms of cancer from developing.

Bottom Line: This study is exciting and will hopefully lead to randomized trials which can prove whether or not taking a statin will prevent prostate cancer.  For now, there is very limited evidence to suggest this would actually work, and men should not start taking a statin just to lower their risk of prostate cancer.