Key words
Colorectal cancer, statins, cholesterol. (Definitions of many terms related to cancer can be found in the Cancer.gov Dictionary.)
Summary
Drugs taken by millions of Americans to lower cholesterol may also reduce the risk of colorectal cancer, a new study suggests. It is too early, however, to recommend that people take the drugs – known as statins – in the hope of avoiding colorectal cancer.
Source
American Society of Clinical Oncology annual meeting, New Orleans, June 6, 2004.
Background
Statins are the most frequently prescribed medications in the United States. The drugs work by blocking an enzyme known as HMG-CoA, which the body needs to make cholesterol. Studies have shown that the drugs also inhibit the growth of colon cancer cells grown in the laboratory. In one earlier randomized clinical trial involving patients who had had heart attacks, the use of statins seemed to be associated with a reduced risk of colorectal cancer.
The Study
In this
observational study, researchers from the University of Michigan, working with researchers in Israel, compared the use of statin drugs among 1,608 Israeli patients who were diagnosed with colorectal cancer and 1,734 other people who were matched for age, sex, and ethnicity with the cancer patients but who did not have the disease.
Study participants, whose average age was about 70, were asked about their personal and family history of cancer, cancer screening practices, other medical conditions, medications taken for at least five years, physical activity, and diet. Eight percent of participants (267 people) reported using statins for at least five years.
Researchers confirmed the use of the drugs by checking participants’ prescription records. They also used statistical techniques to reduce the possibility that the study’s results could be biased by factors known to influence colorectal cancer risk. Such factors are called confounders.
For example, people who are over age 50, who have high cholesterol levels, and who carry a specific mutation in a gene known as APC, are at higher risk for colorectal cancer. Conversely, studies have shown that the use of aspirin or medications known as nonsteroidal anti-inflammatory drugs is associated with a reduction in colorectal cancer risk.
Results
After adjusting for confounding factors, the researchers found that statin use was associated with a 46 percent reduction in the risk of colorectal cancer.
Most (95 percent) of the study participants who used statins took either pravastatin (Pravachol®) or simvastatin (Zocor®). Both drugs seemed to offer a similar protective effect, said senior author Stephen B. Gruber, M.D., Ph.D., MPH, of the University of Michigan Comprehensive Cancer Center.
Equal levels of risk reduction were seen in people who were at high risk of colorectal cancer because of a family history of the disease and in those with no family history of colorectal cancer, Gruber added. However, no reduction in colorectal cancer risk was seen among study participants who took non-statin cholesterol-lowering drugs.
Limitations
This was an observational study, not a
randomized controlled clinical trial, cautioned Gruber. For this reason, the results cannot be the basis for recommending that individuals start taking statins to reduce their risk of colorectal cancer. Statins are approved by the U.S. Food and Drug Administration for cholesterol reduction, not for prevention of colorectal cancer, he said.
Although these findings are promising, they must be confirmed in additional observational studies as well as clinical trials, says Ernie Hawk, M.D., of the Division of Cancer Prevention at the National Cancer Institute (NCI).
Comments
Despite these limitations, the study findings provide the strongest evidence to date that statins may reduce the risk of colorectal cancer, said Gruber. “This is really exciting,” he said. “We are optimistic that these findings will lead to further studies that will allow us to figure out where and how to use these drugs” to prevent colorectal cancer.
The next logical step, he said, would be to conduct a clinical trial designed to find out whether statins reduce risk for colorectal cancer in individuals who are at high risk for the disease because of their family history. Plans are underway to perform such a trial, he added.
According to Hawk, people at high risk for colorectal cancer because of precancerous polyps will soon be asked to join a phase II NCI-supported clinical trial investigating whether statins help to prevent the onset of the disease.
Some findings from laboratory and animal studies suggest that statins may also reduce risk for other cancers, particularly breast cancer and malignant melanoma (the most deadly form of skin cancer), Gruber said. The results of the current study provide a firm basis for other researchers to conduct studies that examine the potential for statins to prevent other types of cancer, he said.
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