A study published in today's Annals of Internal Medicine finds that patients who underwent computed tomography (CT) screenings were twice as likely to have a false positive diagnosis as patients who had a standard chest X-ray. About one in five patients who underwent a CT scan were erroneously diagnosed with lung cancer, compared to one in 10 who had a chest X-ray.
"Lung cancer is a really deadly disease, the No. 1 cause of cancer death in America," Dr. Whelan says. "So if we could get a test that detects lung cancer very early, it would be a real boon to public health."
Dr. Ross says that early detection of lung cancer is key, so CT scans sound promising in theory. "But 30 and 40 years ago we thought the same thing about chest X-rays, and that didn't work. By the time the cancers were detected the horse was out of the barn. This study, I'm sorry to say, says basically nothing, but it's an important topic to discuss. What I want to know is how many lives were saved by this screening."
The study found seven percent of those with a false-positive result after a CT scan underwent a follow-up medical procedure, but Dr. Ross says that in the real world that number would be even higher. (The study classified false-positives as patients who had a positive test but had not been diagnosed with lung cancer a year later). "If I am a smoker who undergoes a CT scan that found a nodule, I'd say, 'Get it out now,' and hope it's not lung cancer," Dr. Ross says.
Dr. Whelan notes that false positives are anxiety-producing and psychologically taxing. "We don't encourage former smokers to get these tests, because they can cause more trouble than they're worth."
"We're willing to accept false positives if it saves lives," says Dr. Ross. But whether CT scans are useful when it comes to detecting early lung cancer has yet to be proven. A large study is now underway to assess CT screening as a life-saving method, but the results won't be available for two years.