Stool test good to catch cancer

Inexpensive faecal occult blood tests (FOBT) are effective for colon cancer screening, a study confirms.

Advances in the stool tests in recent years have made them more effective. The newer immunochemical FOBT (iFOBT) is supposed to detect colon growths more accurately than the older guaiac FOBT - which often picked up bleeding originating in the upper digestive tract.

Immunochemical FOBT is now largely replacing the older test. But there's been surprisingly little evidence that it really is highly specific to colon cancer, according to Dr Yi-Chia Lee of National Taiwan University Hospital, one of the researchers on the new study.

So as reported online in the Canadian Medical Association Journal, the researchers followed nearly 2,800 adults who all volunteered to have iFOBT, a colonoscopy and an upper endoscopy.

Of the 2796 participants, 397 (14.2%) had a positive faecal test result. Out of 28 people confirmed to have colon tumours after a colonoscopy, all but one had a positive iFOBT result.

"It means that almost every case with colon cancer can be identified by iFOBT," Dr Lee said. "It is a strong support to iFOBT as an effective screening tool."

Figures of research

The researchers also found that iFOBT had sensitivity for predicting lesions in the lower gastrointestinal tract of 24.3%, a specificity of 89.0%, a positive predictive value of 41.3%, a negative predictive value of 78.7%, a positive likelihood ratio of 2.22, a negative likelihood ratio of 0.85 and an accuracy of 73.4%.

Of three study participants who were found to have cancers of the stomach or oesophagus, none had a positive result on the iFOBT test.

Among the risk factors for false-positives were the use of anticoagulants and low levels of haemoglobin.

FOBT on its own can't prevent cancer, whereas colonoscopy has the advantage of allowing doctors to spot and remove pre-cancerous polyps.

But as far as cutting the risk of death from colon cancer, stool testing is similarly effective, according to the US Preventive Services Task Force.

And it's much cheaper: iFOBT is more expensive than the older stool tests, but it is still roughly $30, about R200. A screening colonoscopy averages around $3,000, about R20,000.

The downside of iFOBT being specific to colon tumours is that it is not useful for catching cancers of the stomach or throat.

That's particularly important in Asia, where those cancers are common.

Dr Lee said researchers there are looking into whether combining iFOBT with the older guaiac test is useful for catching cancers in the lower and upper digestive tract -- and whether adding a third stool test, which looks for Helicobacter pylori, can help as well.

In the US, cancers of the upper digestive tract are relatively uncommon. The average American has a one in 200 chance of developing oesophageal cancer, while the risk of stomach cancer is one in 114.

In contrast, Americans' lifetime risk of colon cancer is about one in 19, according to the American Cancer Society. More than 50,000 Americans died of the disease in 2010.

(Reuters Health, Amy Norton, July 2011) 

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