Medically Reviewed by Louise Chang, MD on March 06, 2007 From the WebMD Archives
March 6, 2007 — CT scans that look for signs of early lung cancer don’t seem to help current and former smokers avoid death, but they do increase the risk of unneeded surgery, biopsies, and radiation, a new study reports.
The finding comes from four years of follow-up data on 3,246 smokers and ex-smokers screened at medical centers in the U.S. and Italy.
It completely contradicts a study published last October, which seemed to find a huge benefit from CT screening for lung cancer.
Researchers Peter B. Bach, MD, of New York’s Memorial Sloan-Kettering Cancer Center, and colleagues compared the actual number of advanced lung cancer cases and lung cancer deaths to the number predicted by a sophisticated computer model.
The patients in their study had gotten CT scans before they had any sign of lung cancer.
The scans led to 144 diagnosed cases of lung cancer, although the computer model predicted only 44.5 cases.
Of the 144 patients with scans positive for cancer, 109 underwent lung surgery.
But among all the screened patients, in the end 42 cases of advanced lung cancer were found — compared to the 33.4 predicted by the computer.
And, despite the CT screening and subsequent treatment, virtually the same number of patients died as the computer predicted would have died without screening — 38 of the screened patients, versus 38.8 predicted by the computer model.
“Patients should know two things about this study: First, nobody is more disappointed than we are,” Bach tells WebMD. “And second, this is not the last word on the subject. There are two large clinical trials looking at this issue, one [funded by] the National Cancer Institute and the other in the Netherlands.”
But the Bach team’s findings are sobering, says William C. Black, MD, of Dartmouth-Hitchcock Medical Center in Lebanon, N.H. Black is co-author of an editorial published alongside the Bach study in the March 7 issue of The Journal of the American Medical Association. He’s also an investigator in one of the clinical trials of CT lung cancer screening mentioned by Bach.
“The real bottom line is we simply don’t know yet whether CT screening for lung cancer will cause more benefit than harm,” Black tells WebMD. “We have two studies to date that show extremely conflicting results. Both have problems.”
Big Risks From CT Screening for Lung Cancer
It’s already been shown that using chest X-rays to screen symptom-free smokers for lung cancer does not result in fewer lung cancer deaths.
But researchers have been hoping CT scans would work better.
CT stands for computed tomography. It’s a sophisticated, computer-assisted technique that gives doctors a much better look at an organ than an X-ray.
When used for screening, doctors set the CT scan to deliver only low-dose radiation. But that’s still seven or eight times the radiation you’d get from an X-ray, Bach says.
“When abnormalities are found on low-dose CT scans — which happens in 15% to 50% of smokers — more CT scans are done, and those are full-dose scans,” he says. “And 12% of these people end up having biopsies for tumors that turn out to be benign — because the actual cancer rate is south of 1%.”
Also, Bach says that many of the 1% of patients who seem to have malignant tumors actually have only benign growths that, if undetected, would never become deadly tumors. But because doctors can’t say for sure which early cancers will turn deadly, nearly all of them mean lung surgery.
More Surgeries
In earlier studies, X-ray screening for lung cancer didn’t just fail to prevent lung cancer death. It also increased the rate of lung cancer diagnosis by 50%. Bach says CT scans increase the rate of diagnosis by 300% — and lead to a tenfold increase in the number of lung surgeries. Yet his data suggest no lives are saved.
“This means we are exposing patients to radiation, biopsies, and surgeries with highly uncertain clinical benefits,” he says.
And then there is the anxiety caused by having an abnormality found.
“So say you have an abnormal finding on CT, and your doctor says, ‘Oh, we don’t know what it is, come back in six months,'” Bach says. “If the CT scan screening were effective, and we were going to save lives, we could work with patients on managing this anxiety-creating test. But we should not subject people to such tests when we have no objective evidence it will help them.”
But what about the relief you might feel if your CT scan is normal? Bach says this is false reassurance.
“If you don’t show positive on a screening CT scan, there is no guarantee you won’t die of lung cancer,” he says. “I don’t want people to get the idea that we can rule out cancer.”
How to Get a CT Scan for Lung Cancer Screening
Bach and Black note that while there’s no proof CT scans save the lives of current and former smokers, there’s also no proof they don’t.
That proof may be on the way. But Black says it won’t get here before the end of 2009, when results from the National Cancer Institute trial are expected.
Meanwhile, patients interested in CT scans should talk to their doctors.
“Most credible places will not accept a self-referral. Our institution, for example, will accept a screening CT scan referral from a doctor only if the doctor assures us he or she understands he knows how this works,” Black says. “We have done a handful of patients at our institution, but only when we knew the doctor understood that we don’t know if it works, and only if the patient understands the risks.”
The center performing the scans must do two things. First, there must be a knowledgeable person who speaks with you beforehand about the risks — and who offers you a chance to decide you don’t want to do it. And second, the site must have a well-established protocol for interpreting the results.
The National Cancer Institute web site — cancer.gov — offers a discussion of the pros and cons of CT screening for lung cancer.
