A blood test for cancer? Don’t hold your breath.
Submitted by Dr.Kattlove’s Cancer Blog
I thought of this when I read a paper that reviewed 93 articles that looked at the success rate of blood tests to detect colorectal cancer. So far no breakthroughs.
We’ve been looking for a blood test to find cancer early for many years. And, many have been found that will spot different types of cancer, but almost never in its earlier stages. The first test that gained wide use was the CEA (carcinoembryonic antigen). CEA is a protein made in excessive amounts by the cancer cell. At first, it was found to be elevated in the blood of people with widespread colorectal cancer. But then researchers learned that its blood level can be high in people with many other types of cancers.
Specific blood tests have been sought for other cancers. Probably no cancer has been scrutinized more than ovarian cancer, mainly because this cancer tends to grow in women without producing symptoms until it is usually too late to be cured. Ovarian cancer does produce a marker, called CA-125, that appears in the blood. Unfortunately, when it does, the cancer is usually too advanced to be cured. Many studies have tried using this as a screening tool, but the test is not sensitive enough to find the cancer in its earliest stages.
A few years ago, researchers from the National Cancer Institute in the U.S. came up with a “proteonomic” test for ovarian cancer. Proteonomics looks at the patterns of proteins in the blood. It is kind of complex and requires elaborate testing. But, these NCI researchers seemed to find abnormalities in the blood of women with early stage ovarian cancer and it looked like a major breakthrough. But others couldn’t replicate their results. Also, it turned out that the original researchers had patented their test and started a company to market it. Several years later, we still haven’t heard from them. Good marketing, bad science, it seems.
Blood tests for cancer are useful though. If someone has a cancer that has spread and is being treated, following the blood test often tells us whether the cancer is responding. This is a lot easier than CT scans and other cumbersome tests. But sorry to say, these are only worth doing in people with advanced cancer. They have little use in its earliest stages.
So, keep up the screening tests like colonoscopy, pap smears, mammograms and try to stay healthy.
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