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Thursday, 31 January, 2002, 02:49 GMT
Gene test hope for bowel cancer
The genetic test has proved highly reliable
The genetic test has proved highly reliable
Doctors have devised genetic tests that should improve detection of bowel cancers.

One accurately spots early signs of colon cancer at a stage where it can still be cured.

The second allows doctors to spot a particular kind of colon cancer that is normally hard to detect without invasive techniques.

Both tests have been developed by Kimmel Cancer Center at Johns Hopkins, Baltimore, Maryland.

If colon cancer is detected before it has spread to other tissues and organs, it can be cured in up to 90% of cases.

In the UK in 1997 34,310 people were diagnosed with bowel cancers.

Early detection

The test which picks up early signs of colon cancer detects a genetic mutation which occurs in the DNA of patients with the disease.

Doctors pioneering the test say it is "exquisitely specific", and believe it could be widely available within three to five years.


These early results look promising

Dr Mary Berrington, Cancer Research Campaign
The test picks up mutations in the APC gene.

APC gene mutations are present in nearly every cancer, and just as mutated gene copies are shed into the stool, so are normal copies.

It has taken over 10 years since the role of the mutated gene was identified for the technology to identify it in stools to be developed.

The APC mutation occurs just once in every 250 genes, and there are thousands of possible mutations.

To overcome this, the researchers developed a process called Digital Protein Truncation (Dig-PT).

This means they can separate small portions of extracted DNA where mutated copies stand out more clearly.

In this study, stool samples from 74 patients were examined. Twenty-eight had early colon cancer, 18 had adenomas, premalignant colon tumours and 28 had no disease.

Of those with early colon cancer, 61% had the telltale mutation.

Half those with premalignant adenomas also had it, but it was present in none of those who were disease-free.

The researchers also found there were no false positive results - where cancer is inaccurately thought to be present.

Dr Kenneth Kinzler who led the research, which is published in the New England Journal of Medicine, said: "We still have a way to go before we can confidently use such a screening test in the general population, but we are encouraged by the fact that we've detected mutations in a significant fraction of the patients with early stage tumours and never in people free of disease."

Hard-to-detect tumours

The second test developed by the centre identifies a separate genetic mutation, and could aid detection of proximal colorectal cancers.

These are normally the hardest tumours to detect as they are furthest from the anus.

Researchers say the new test, when combined with a sigmoidoscopy, (an examination of the sigmoid section of the colon) or other DNA-based tests, could replace the more difficult and expensive colonoscopy procedure, where a fibre-optic tube is used to examine the area.

The test focuses on mutations of the BAT26 gene, another marker for colorectal cancer.

The Kimmel Center team examined stool samples from 134 patients, 46 of whom were known to have cancers in the proximal colon.

'Compelling'

Eighteen of the 46 had BAT26 alterations in their tumours, and in 17 of the 18, that could be identified by faecal DNA assessment.

Professor Bert Vogelstein who led the research said: "These results provide compelling evidence that mutations in stool can be used to identify patients with proximal cancers.

"The high specificity of the analysis, with zero false positives, was very encouraging.

"We hope that this approach will provide an important addition to the options available for reliable, non-invasive detection of curable colorectal cancers."

The research is published in the and the Lancet.

Dr Mary Berrington of the Cancer Research Campaign, said: "These early results look promising. If they hold true in larger studies, this non-invasive approach could prove an important addition to existing methods for the early detection of bowel cancer.

"Bowel cancer is very common, but when found early there is a very good chance of cure."

See also:

25 Oct 01 | Health
Call for colon cancer screening
01 Apr 01 | Health
Survey highlights 'taboo' cancer
20 Jul 00 | Health
Probe 'could miss early cancer'
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