The latest recommendations on screening for colorectal cancer, released on Wednesday, include some new bits: You can have a virtual colonoscopy (no huge tube snaking its way up your insides), even 85-year-olds might benefit from being screened, and a novel test to detect DNA in fecal samples gets a thumbs-up.
But the guidelines, issued by a panel of experts who advise the US government on preventive care, still leave one very big elephant in the room — no type of colorectal cancer screening has been shown to reduce mortality overall. Here’s what to take note of:
1. Colonoscopy goes virtual
For the first time, the US Preventive Services Task Force gave a thumbs up to computed tomography colonography, popularly known as a virtual colonoscopy. Patients still need to avoid solid foods for two or three days beforehand and use an enema to empty their bowels, but because a tube is inserted only to blow air into the colon (not snake its way up several feet), some find it less uncomfortable.
A CT or MRI takes images of the air-filled colon, looking for pre-cancerous polyps. Any that are found must be removed via standard colonoscopy. Studies show that CTC detects 73 to 98 percent of pre-cancerous polyps 6 millimeters (about one-quarter inch) across or larger, compared to 75 percent to 93 percent for standard colonoscopy. When the virtual version identifies a problem, it is correct in 89 percent to 91 percent of cases (the remaining 10 percent or so are “false positives”), compared to essentially 100 percent for standard colonoscopy.
One significant benefit of going virtual: no chance of the colonoscope perforating the colon, as occurs in 4 out of 10,000 colonoscopies. Another: It might get more people screened for a disease that will kill 49,190 people in the United States this year but is largely preventable if caught early.
2. DNA also works
Fecal tests, which look for blood in stool, again got a thumbs-up from the task force, reinforcing the fact that colonoscopy is not the “gold standard” for colorectal cancer screening. The most common and best-studied fecal screening, called fecal immunochemical tests, detected 73 percent to 88 percent of pre-cancerous polyps, the task force reported in a paper in the Journal of the American Medical Association accompanying its recommendations. Although that’s lower than a colonoscopy, fecal tests are done every year and so are equally good at preventing deaths from colorectal cancer. They are also slightly less likely to rise false alarms.
Adding a second test that specifically finds cancer-associated DNA improves the sensitivity slightly, the task force said, though it also raises the number of false alarms. The one such DNA test is called Cologuard. “We’re pleased with the clarity of these recommendations and expect they will expand and promote utilization of Cologuard as an innovative colon cancer screening option,” said Kevin Conroy, CEO of manufacturer Exact Sciences.
3. Make an appointment for grandpa
The task force unequivocally recommends screening for everyone from 50 to 75. But unlike the 2008 recommendation against screening people 75 or older (except in unusual cases), this time the task force concluded that some 76-to-85-year-olds might benefit.
In particular, those who are healthy and have never been screened might have undetected pre-cancerous polyps whose removal could keep them from dying of colorectal cancer. “Age itself should never be a hard cut-off,” said Dr. Vinay Prasad, an oncologist and cancer researcher at Oregon Health and Sciences University who was not involved in the task force. “There are some 76-year-olds who are in excellent physical shape” and might benefit from screening, “but if you have been screened several times before it’s unlikely that additional screening [from age 76 to 85] would add benefit.” That’s because it takes about 20 years for a pre-cancerous polyp to become a dangerous colorectal cancer; if nothing was found in a 70-year-old it’s unlikely that something found at age 76 will be fatal before something else is.
4. But … you still won’t live forever
Although studies have found that screening reduces one’s risk of dying of colorectal cancer by 14 to 28 percent, it doesn’t reduce overall mortality — that is, deaths from all causes — the task force acknowledged. In other words, over any given period, deaths among people who have undergone the screening are no less than among those who have not. The reason, said Prasad, may be that the lives saved by early cancer detection are somehow balanced by an equal number of lives lost due to something else, including the intense and sometimes toxic therapies that follow such detection.
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