Scientists at the Johns Hopkins University say they've found that a protein used to predict heart disease may also be a warning sign for colon cancer, a disease that afflicts 150,000 Americans and kills 50,000 annually.
High levels of C-reactive protein, or CRP, in a patient's blood "could become a very good early marker" for predicting the colon disorder, said Northwestern University cancer specialist Dr. Boris Pasche.
The findings also bolster the theory that inflammation plays a role in some cancers, as well as a host of other chronic ailments, including heart disease and diabetes.
The Hopkins researchers, who published their report today in the Journal of the American Medical Association, analyzed blood samples from a long-term study of people in Washington County.
They compared 131 people who got colon cancer with 262 people who did not. "People with high levels of CRP had a significantly higher risk of developing colon cancer sometime in the future," said Dr. Thomas Erlinger, the study's lead author.
An epidemiologist at Johns Hopkins School of Medicine and Bloomberg School of Public Health, Erlinger noted that the blood samples were typically taken years before the people were diagnosed with cancer.
Researchers aren't sure whether CRP has a role in causing cancer, or if it simply is a marker for disease-related inflammation.
Scientists elsewhere praised the work. "It's a rigorous study. It's a feather in their cap," said Harvard Medical School biochemist Charles N. Serhan.
In an editorial accompanying the paper, Serhan and Pasche say the study could point the way to new cancer therapies involving anti-inflammatory treatments.
But others were more skeptical of the paper's conclusions. "It's interesting, but it requires careful confirmation," said Dr. Paul Ridker, a cardiologist and professor of medicine at Harvard Medical School.
A pioneer in CRP research, Ridker was the first to connect high levels of the protein to heart disease. But he cautioned that "cancer data is very tricky," and said research by his lab had not found a link between CRP and cancer.
Scientists have long suspected that inflammation plays a part in colon cancer, noting that patients with inflammatory bowel disorder have a higher risk of the disease.
But Erlinger's study is the first to link cancer with CRP. Discovered in 1929, the protein is known to be involved in the body's inflammatory response. Over the past several years, CRP has become a hot research topic: High levels of the protein have been linked to a range of ailments, including heart attacks, stroke and diabetes.
Produced primarily by the liver, CRP plays a role in triggering inflammation. It rises significantly in response to acute injury or illness, as the body uses inflammation to fight off infections and other threats. When attacked by a flu virus, for example, the body's immune system often responds with a generalized inflammation - fever - to battle microbes. During and right after a flu, CRP levels increase.
But in recent years, researchers have realized that many chronic conditions also boost CRP levels - often before other symptoms appear. Much of this research has involved heart disease. Ridker and others have shown conclusively that increased CRP levels can predict heart attacks and strokes.
Last year, the American Heart Association and the federal Centers for Disease Control and Prevention recommended that patients at moderate or high risk for heart disease should have their CRP levels tested. Ridker argues that such tests are so useful that they should be used more widely.
In 2002, for example, German researchers found increased CRP levels among subjects who developed Alzheimer's. Blood samples in that study were taken decades before subjects showed overt symptoms. Last year, scientists at Yale and Emory universities reported a connection between depression and elevated CRP.
Ironically, as CRP is linked with more ailments, its value as a warning sign could decrease. High CRP levels could indicate anything from Alzheimer's to atherosclerosis.
"It's like smoke going up - you know there's a fire somewhere, but you don't know where," said Serhan.
The interest in CRP research dovetails with another relatively new concept, that inflammation may be the ultimate culprit in a range of chronic ailments.
"What is emerging is that inflammation plays a major role in a lot of diseases, including Alzheimer's, heart disease and diabetes," said Claudio Franceschi, professor of immunology at the University of Bologna in Italy. A leading proponent of this hypothesis, he is now examining the role of inflammation in colon cancer.
Erlinger, now looking at whether CRP can predict other types of cancers, said it is too early to tell whether the colon cancer study will change medical practice.
"I wouldn't recommend that people run out to get a CRP test to find out their cancer risk," he said. "There is still a long way to go before we figure out how to use this clinically."