Late in July, the FDA approved a blood test to detect colon cancer. What does this mean for you?
Colon cancer is the second most common cause of cancer deaths in adults, behind only lung, and an estimated 53,000 people will die of colon cancer in the U.S. this year. At the same time, colon cancer should be almost completely curable if found very early and surgically removed.
Finding cancers in people without symptoms is called “screening,” and good screening tests are only available for a small number of cancers. Good screening tests should pick up cancers early, should be negative in people without the disease and should be proven to reduce death rates in screened populations.
For colon cancer, the gold standard screening test is the colonoscopy. It will detect both cancer and precancerous polyps, most of which can be removed during the procedure. It is very sensitive – if the person has done a good clean-out “prep,” very few polyps or early cancers will be missed. It does not give false alarms – if your colon is normal, the endoscopist sees this and you can generally go 8-10 years before your next test.
The downsides are cost and the “ick” factor.
A recent report on the cost of cancer screening showed that fully 60% of the cost of all cancer screenings was spent on colonoscopies. The test requires a whole team, a special room like an operating room, anesthesia for most people having the test and costs thousands of dollars.
As Dave Barry so colorfully described (miamiherald.com/living/liv-columns-blogs/dave-barry/article1928847.html), the thought of a colonoscopy is repulsive to many of us, and the dietary and laxative preparation required is a turnoff for many.
The alternative has been to check the stool for hidden bleeding, the so-called FIT test. If done every year, this has a reasonably good pickup if positive tests are followed by colonoscopy. More recently, a stool test looking at cancer DNA markers has been approved. It picks up about 85% to 90% of colon cancers but only about 40% of large polyps.
The newly approved blood test looks for circulating cancer DNA and was shown to detect about 83% of cancers found on colonoscopies. It had a “false positive” rate of 10%, meaning 10% of people with a positive blood test had no cancer. And it was poor at finding precancerous polyps. Only some 13% of people with such polyps had a positive test.
The big advantage of the new test is ease – most of us are used to having blood drawn at a medical visit and do not mind having this done. No preparation is needed. The cost is dramatically lower than a colonoscopy. The biggest disadvantage is that it is not as good as a colonoscopy. It will miss most precancerous polyps.
My take: If you have insurance that covers a colonoscopy, gather up your courage and just have it done.
If the alternative is not getting screened, do the blood test.
Edward Hoffer MD is Associate Professor of Medicine, part-time, at Harvard.
What Does The Doctor Say?
By Dr. Edward Hoffer