Colonoscopy the best way to de­tect colon can­cer

Daily Freeman (Kingston, NY) - - YOUR DAILY BREAK - An­thony Ko­maroff

DEAR DOC­TOR K »

I heard about a new home test that de­tects colon can­cer. Is it a good al­ter­na­tive to colonoscopy?

DEAR READER »

The new test ap­pears to be an ad­vance, but I don’t think it’s as good as colonoscopy. Par­tic­u­larly for peo­ple who are at higher risk for colon can­cer, I re­gard colonoscopy as the best test.

Colon (or col­orec­tal) can­cer lies in the wall of the colon. It can cause pain­less bleed­ing. The amount of blood can be so small (“oc­cult blood”) that it isn’t vis­i­ble in the bowel move­ment, but it can be de­tected by chem­i­cal tests. Per­form­ing these tests for blood in the bowel move­ment — fe­cal oc­cult blood tests — has been a tra­di­tional way of try­ing to catch colon can­cer early.

How­ever, colonoscopy re­mains the best way for catch­ing col­orec­tal can­cer early. This test, done un­der se­da­tion, uses an in­stru­ment to look inside the colon. A sim­i­lar pro­ce­dure, flex­i­ble sig­moi­doscopy, looks at about half of the colon and doesn’t re­quire se­da­tion. These tests not only can see can­cer, but also ab­nor­mal­i­ties (ade­no­mas) that can be­come can­cer­ous in the future. The tests also al­low the ade­no­mas and some very early can­cers to be re­moved dur­ing the test.

In Au­gust 2014, the FDA ap­proved Co­lo­guard, a new test for col­orec­tal can­cer. The Co­lo­guard test is done at home. You col­lect a stool sam­ple and mail it to a lab­o­ra­tory for anal­y­sis. Like the fe­cal oc­cult test, it checks for blood in stool. But the new test also looks for ab­nor­mal DNA.

Colon can­cers de­velop be­cause genes in the cells lin­ing the colon have de­vel­oped mu­ta­tions. The ab­nor­mal DNA caused by these mu­ta­tions, like oc­cult blood, is shed in the bowel move­ment. That ab­nor­mal DNA can now be de­tected by spe­cial tests.

One large study of nearly 10,000 peo­ple found the new test to be very ef­fec­tive. Peo­ple in the study were given a fe­cal oc­cult blood test, the Co­lo­guard test and a colonoscopy. Co­lo­guard de­tected 92 per­cent of the can­cers that colonoscopy found; the fe­cal oc­cult test de­tected 74 per­cent. Co­lo­guard also found 69 per­cent of the polyps that were con­sid­ered most likely to turn into can­cer. The fe­cal oc­cult test found 46 per­cent.

On the down side, the Co­lo­guard test pro­duced more false pos­i­tives than the fe­cal oc­cult test. A false pos­i­tive test says there is a polyp or can­cer when none ac­tu­ally ex­ists — and that re­quires fur­ther in­ves­ti­ga­tion with a colonoscopy to con­firm or rule out the di­ag­no­sis.

The new Co­lo­guard was ap­proved for screen­ing in peo­ple ages 50 to 85 who have an av­er­age risk of colon can­cer. It is not meant as a sub­sti­tute for colonoscopy if you have a greater-than-av­er­age risk. This in­cludes peo­ple with:

• A history of polyps or prior col­orec­tal can­cer;

• A strong fam­ily history of col­orec­tal can­cer;

• Ul­cer­a­tive coli­tis or Crohn’s dis­ease.

Co­lo­guard of­fers an­other op­tion for col­orec­tal can­cer screen­ing. But right now, colonoscopy still re­mains the best screen­ing method. It is rec­om­mended once ev­ery 10 years for peo­ple age 50 and over who have an av­er­age risk of col­orec­tal can­cer.

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