October 31, 2010
Home Colon Cancer DNA Tests Under Development

One of the biggest benefits from the continuing plunge in DNA testing costs is going to be earlier diagnosis of cancers. One DNA test under development for colon cancer detection will be usable at home.

David Ahlquist, M.D., professor of medicine and a consultant in gastroenterology at the Mayo Clinic in Rochester, said much of that low rate may be due to inconveniences associated with conventional approaches.

"There is definitely an incentive and legitimate justification to be designing a screening approach that is user friendly, affordable and has the ability to detect pre-cancers," said Ahlquist. "The noninvasive stool DNA test we have developed is simple for patients, involves no diet or medication restriction, no unpleasant bowel preparation, and no lost work time, as it can be done from home. Positive tests results would be followed up with colonoscopy."

Some might think "home stool DNA tester, how gross". But I'll tell you what's gross: watching an adult you've known and loved for years experiencing excruciating pain from cancer metastases throughout their bones while they lose so much weight that they shrink up to skin-and-bones worse than concentration camp survivors.

The test that Ahlquist and colleagues evaluated is under development by Exact Sciences, a molecular diagnostics company in Wisconsin.

The test, which is not yet approved by the FDA, is conducted using a stool sample and works by detecting tumor-specific DNA alterations in cells that are shed into the stool from pre-cancerous or cancerous lesions.

As Nicholas Wade reports, the Exact Sciences test is one of two colon cancer DNA tests headed to market. The second test would require a blood sample.

The other test looks in blood for changes in a single gene, called Septin 9, which is not in the Exact Sciencesí panel of four genes. The test has been developed by Epigenomics AG in Germany. Both tests would be less expensive than colonoscopy, and potentially more effective. Compliance with colonoscopy is low, since people donít want to have one, and the overall cost per detection is high because most people are healthy, and even colonoscopy misses many tumors in the upper part of the intestine.

Click thru and read Wade's articles for the caveats. But note that whatever limitations these tests have today they are just the beginning.

You only get colonoscopy results when you go to the trouble, cost, and small but real risk of getting a colonoscopy. Whereas a home DNA test would cost much less and could be done much more often. The higher frequency of testing would in theory catch the cancer at a much earlier stage. Once the home DNA test turns up positive the person could go in for a colonoscopy to remove polyps or other growths.

Since some cancers develop literally over almost 2 decades early diagnosis opens up the potential of finding and removing cancers long before they become life threatening. Once home tests of blood and saliva for DNA (and likely for antigens) to detect cancer become cheap and widely available the challenge is going to be to find the early stage cancers. Early stage means they will be small. How to find them?

If the tests can narrow down the cancer source to a single organ then excising the cancerous tissue might not be continue to be necessary. Eventually we'll be able go in for new replacement organs. If a test could, for example, indicate presence of a pancreatic cancer 10 years before it will metastasize then in 2030 the solution might be to start growing a new one in a lab. Get the new one after 6 months or a year and toss out the old one.

Share |      Randall Parker, 2010 October 31 07:16 PM  Biotech Cancer


Comments
PacRim Jim said at October 31, 2010 11:15 PM:

I want a colon cancer app for my iPhone.

jpstraley said at November 1, 2010 6:57 AM:

Key is false positives. If a disease occurs 1 in 100 persons, but the test has a 1% false positive rate, 9 of the 10 hits are misleading.

Phillep Harding said at November 1, 2010 1:49 PM:

I say, "Put up with the false positives, in order to avoid bone cancer. Tumors in the bone HURT!"

BTDT, sit funny.

Nick G said at November 1, 2010 3:49 PM:

jpstraley,

I think you mean if the test has a 10% false positive rate.

You're correct, but it would still reduce the number of colonoscopies by 90%. Remember, right now everyone is supposed to get a test.

LAG said at November 2, 2010 12:53 PM:

The problem is not false positives. Those results are simply inconvenient if scary for the time it takes to get a clinical test. The problem is the false negative that keeps you from further treatment, because, well, the test just told you that you were cancer-free. The delay in obtaining an accurate diagnosis is the equivalent to a death sentence. If you want to know how well the company trusts their test, check out how much liability insurance they plan to carry to cover that eventuality.

Larry J said at November 2, 2010 1:16 PM:

Three years ago, I had a colonoscopy. They found and removed pre-cancerous polyps. That got my attention. Next week, I'm having another colonoscopy. The prep for the test is not pleasant but the test itself is completely painless and quick. If you're 50 or older, get the test. It isn't that big a deal but could save your life. Don't be a wuss.

Three weeks ago, one of my brothers was diagnosed with an extremely rare and aggressive t-cell lymphoma that has spread throughout his body. He was sick 3 years ago but the doctors couldn't find out what was wrong with him. Now they know. At this point, I'm open to just about any screening test.

Nick G said at November 3, 2010 10:40 AM:

The problem is the false negative

I agree. On the other hand, it's worth noting that colonoscopies have false negatives too, and that rate is at least as high as the rates given for the stool and blood tests.

Who knows? The apparent false positives in this study may have been caused by false negatives in the colonoscopies used for validation.

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