A Blood Test Instead Of A Colonoscopy?
If only! But as Medcan’s head of endoscopy explains, colon cancer is a bit like Elvis. You’re best to catch it before it leaves the building—which is where a blood test fails.
It’s a Holy Grail for medicine—a blood test for cancer, an easy test that tells you whether you have that dreaded disease. The “Holy Grail” status particularly applies to blood tests for colon and rectal cancer. We’re too busy to get scoped. Can’t we just show up and get scanned, like at the airport? Why can’t they do a blood test for colon cancer?
Ah… but there is! Blood tests for colon cancer exist. They’re well-advertised. So should we cheer and break out the bubbly? Sadly, no. There’s a catch.
Colon cancer affects one in 20 people, which means both men and women have about a 5% lifetime risk for contracting the disease. It’s the number-two cancer killer, after lung cancer. You’re more likely to die from colon cancer than you are from comparative maladies in the breast or prostate. But it also is the best type to find early. Beginning stage-A colon cancers are more than 90% curable. Later-stage cases, known as stage C or D cancers, are so advanced and widespread that they’re nearly always fatal.
So the key is finding this disease early, in its pre-cancer phase. Is the blood test for colon cancer able to do that?
For example, it’d be great if we could just draw a little blood to find out whether a given patient has something like “the gene for colon cancer.” But it turns out that in more than 75% of cases, when someone is found to have colon cancer, there is absolutely no pre-existing family history. In the majority of cases, colon cancer is not a genetic-based disease. So a genetic blood test won’t help in most cases.
Slightly better utility is found in blood tests based on colon cancer “markers”—tiny protein molecules detectable in the bloodstream. The idea is, the doc tests for the tiny traces of the cancer-related protein, and if any are found, then the patient should have colon cancer. Right?
Sorry, no. It’s true that we can detect very early markers of colon cancer in the blood. But the cancer has to have invaded blood vessels for markers to circulate in the blood. And by the time the cancer has invaded the blood vessels, it is too late. The tumor has already extended beyond the bowel. It’s spread. We’re already in stages C or D. The horse has already left the barn. Elvis has left the building.
So a blood test for colon cancer will detect advanced cancer, but by the time the cancer has become advanced, it’s too late. Blood tests are not reliable for picking up early-stage cases—and they’re completely useless for detecting pre-cancer conditions such as colonic polyps. What would be ideal is a blood test that screens for pre-cancerous polyps. Because removing suspicious polyps can dramatically lower colon cancer rates and in many cases can prevent cancer altogether. We want to find Elvis before he was famous, not when he was fat or left the building.
The US Multi-Specialty Task force is a non-partisan group of specialists charged with determining the best screening method for colon cancer. The Task Force picked the colonoscopy as the best test for early detection. A very invasive procedure, yes. But also very useful at detecting pre-cancerous polyps.
So the search for the Holy “GI” Grail continues. We need a simple, non-invasive way of testing and preventing colon cancer. The search continues…. And until then, go for the best screening test available.