Does taking cholesterol-lowering medication help fight cancer? A controversial new study has drawn such a tantalising link. The New England Journal of Medicine recently reported a large study of 295,925 patients showed that the use of statins increased the survival rate of cancer patients. The researchers followed all cancer patients in Denmark diagnosed between 1995 and 2007 and found that those who took the cholesterol-lowering statins before they were diagnosed had a 15 per cent lower risk of dying than those who had not used the drugs. According to one of the study's authors, earlier studies suggested cancer cells need cholesterol to grow. And a lack of cholesterol has been shown to inhibit tumour growth. Thus the question arose if tumour growth would be impeded by the use of cholesterol-lowering drugs.
Statins are a class of drugs used to lower cholesterol levels by inhibiting the enzyme 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase, which plays a central role in the production of cholesterol in the liver. This then inhibits build-up of plaque on artery walls in order to prevent stroke and heart disease. Their genesis is an interesting saga of public health initiative, scientific collaboration, pharmaceutical marketing and paradigm shifts in medicine.
Indeed, the widespread use of statins has been lauded as one of the hallmarks of prescription pattern in the last two decades. Zocor, Lipitor, Crestor became household names and reaped immense profits for the pharmaceutical giants that manufacture them. Lipitor is known as the best-selling drug in pharmaceutical history, with sales exceeding US$125 billion for Pfizer. Side effects of statins include muscle damage, liver injury and diabetes mellitus.
The latest study has generated some interest in the medical community but no one is jumping up and down in excitement and it is certainly no cause to demand a lifelong prescription of statin from your family doctor.
The study was an "observational" study; as opposed to an "interventional" study. Observational studies are meant to study trends and draw associations, rather than conclusions. In other words, they are designed to provide questions whereas interventional studies are designed to provide answers. It must also be remembered that association is not causation. Thus, by virtue of its design, the study did not prove that statins have a direct impact on cancer survival.
There were also some confounding factors that may have impacted on the results. For instance, the use of aspirin and smoking, which have direct beneficial and harmful effects on cancer were not corrected for.
There is another pitfall with this particular observational study; that is the "self-selecting patient" bias. Health conscious and thus healthier patients are mostly like to use statins to begin with as compared with their less-health-conscious counterparts. Thus, the apparent increased cancer survival rate may be due to the subjects' overall health profile.
To further put things into context, this is not the first study examining the effect of statins on cancer. Earlier randomised trials that investigated cardiovascular benefits of statins have not shown any benefit against cancer. In 2002, a controlled, randomised study, known as Prosper, actually showed an increase in cancer risk in elderly patients on statins. In fact, a recent expert opinion published in Current Oncology concluded that there is ample evidence that statins may promote cancer in certain segments of the population; namely, the elderly. When faced with conflicting data, medical scientists perform a meta-analysis, which is a statistical method of combining the results of several studies. In January, a published meta-analysis involving 175,000 subjects from 27 randomised trials of statin therapy showed that statins were not associated with a reduced risk of cancer.
The study authors appropriately commented in their conclusion that their result showed that there is a need for more trials of statins with cancer patients. These trials should be interventional, with standardised patient selection, randomised and controlled in order to provide useful information.
Such a disciplined approach is much needed in interpreting the data, especially when it involves such a commonly used medication, due to its global ramifications.
Dr Ernie Yap practises internal medicine in the US