Blood test might replace colonoscopies.
People with high levels of a particular blood protein may be at increased risk of developing colon cancer, a preliminary study has shown. Such tests might one day spare patients the discomfort of colonoscopy.
The protein, called C-reactive protein or CRP, is involved in inflammation. Thomas Erlinger of Johns Hopkins University in Baltimore, Maryland, and his group found that in a sample of more than 500 people, the 25% with the highest levels of CRP were 2.5 times as likely to develop colon cancer as those who had the lowest levels.
The result raises the prospect that a routine blood test for CRP might identify those who should undergo more intensive surveillance. It might one day prove as useful as blood cholesterol measurements, for example, which help gauge the danger of heart disease.
Before such screening can begin, other researchers must repeat the work to confirm the discovery, cautions Boris Pasche, who studies cancer genetics at Northwestern University?s Feinberg School of Medicine in Chicago, Illinois. But the finding "is an eye-opener", he says.
Cancers of the colon and rectum are the second most common cause of cancer death in the US and UK, after lung cancer. Around 147,000 people were diagnosed with the disease last year in the US alone. They are treated with surgery, radiation and chemotherapy.
One of the best ways to detect tumours is by colonoscopy, in which doctors use a camera on a fibre-optic cable to scan the inside of the bowel for pre-cancerous polyps. The American Cancer Society recommends such an examination once every ten years for those over 50 years old. But colonoscopy is expensive and uncomfortable. "Many patients do not like having a camera put up their behind," says Pasche.
Researchers are hunting for less invasive ways to screen for colon cancers. Last year, for example, a study showed that ?virtual colonoscopies? using computed tomography (CT) scans pick up polyps as successfully as the more intrusive method.
A team at Johns Hopkins University in Baltimore, Maryland, have proposed another method to screen for colon cancer: sifting through faeces for traces of a telltale risk gene. They hope to scan for mutations in the gene, a strong sign that a tumour might be budding.
Erlinger's team studied more than 172 colon cancer patients and a healthy comparison group from a larger medical study cohort. They measured CRP levels in stored blood samples taken in 1989 from the controls and cancer patients.
Researchers remain unclear why high levels of the inflammatory protein would be associated with a high risk of colon tumours. Elevated CRP may simply reflect heightened immune activity, Pasche suggests. The immune system may react to pre-cancerous polyps and trigger their transformation into tumours.
A higher level of CRP is also linked to an increased risk of heart disease and diabetes, so elevated levels might be a more general sign that something is awry in a patient. "They might be predisposed to several chronic diseases," says Erlinger.
Pasche says researchers must now investigate whether monitoring CRP can play a part in cancer prevention. Previous studies have shown that aspirin or other nonsteroidal anti-inflammatory drugs, for example, can cut a person?s risk of developing colon cancer. So researchers should now determine whether patients with high CRP levels respond to those drugs, says Pasche.
Erlinger, T.P., Platz, E.A., Rifai, N. & Helzlsouer, K.J. C-reactive protein and the risk of incident colorectal cancer. Journal of the American Medical Association, 291, 585 - 590, (2004).