High blood levels of a protein linked to heart attacks might also be an early warning sign of colon cancer, a study found.
The substance is C-reactive protein, or CRP, which is produced in the liver in response to infection or inflammation anywhere in the body. In recent years, doctors have come to believe that high levels of CRP in the bloodstream raise the risk of a heart attack by damaging blood vessel walls.
In a study of 22,887 adults, those with the highest levels of CRP were more than twice as likely to develop colon cancer over an 11-year period as those with the lowest CRP levels.
High CRP levels were strongly linked with colon cancer even after other risk factors such as age, family history, being overweight and smoking were taken into account.
The study was led by Dr. Thomas Erlinger of Johns Hopkins Medical Institutions and appears in Wednesday's Journal of the American Medical Association.
People with diseases involving chronic intestinal inflammation, including ulcerative colitis, are known to face an increased colon cancer risk, and studies have shown that aspirin and other anti-inflammatory drugs can reduce that risk.
The new findings suggest that elevated CRP levels might be a risk factor even without overt signs of colon inflammation, though Erlinger said it would be premature to recommend testing CRP as a way to predict a person's colon cancer risk.
"It will be important for future research to focus on whether and how CRP measurement could be used to improve current screening and prevention strategies,'' he said.
The researchers examined medical records of mostly white adults in Washington County, Md., taking part in an unrelated study.
Colon cancer was diagnosed in 131 people during the study. Twenty of the diagnosed patients had the lowest initial CRP levels. By contrast, 50 colon cancer patients had CRP levels in the highest range.
Colon cancer will be diagnosed in more than 100,000 people this year, according to the American Cancer Society. It is one of the most common types of cancer in industrialized nations.
Screening tests include colonoscopies, which allow doctors to examine the entire colon through a narrow tube. Eating lots of fruits and vegetables, avoiding smoking and fatty foods, and getting plenty of exercise can lower the risk of colon cancer.
In an accompanying editorial, experts noted that the study does not rule out the possibility that high CRP levels are a consequence of early colon cancer rather than a risk factor for the later development of cancer.
Giving aspirin to people with high CRP and watching the outcome could clarify the issue, said cancer specialist Dr. Boris Pasche at Chicago's Northwestern University and researcher Charles Serhan at Harvard's Brigham and Women's Hospital.