CT Scans Cut Lung Cancer Deaths, Study Finds
Article date: November 4, 2010
By Karen Patterson
A massive clinical trial has identified a type of CT scanning as the first screening test that can reduce deaths from lung cancer, the most common cause of cancer deaths in the United States and worldwide.
Among older people with a long history of heavy smoking, the noninvasive test—called low-dose helical (or spiral) CT scanning—reduced the odds of lung cancer death by 20%, compared with screening by a simple chest x-ray, said Dr. Harold Varmus, director of the National Cancer Institute.
Calling it an important moment for public health, Dr. Varmus predicted the finding will help fuel efforts to protect “the tens of millions of former and current smokers in this country against the lethality of lung cancer.” Initial results of the study, which is called the National Lung Screening Trial, were reported in a news conference in Bethesda, Md., on Nov. 4.
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Statistically significant difference in death rates
The study found that 442 deaths from lung cancer had occurred among participants receiving the chest x-rays, compared with only 354 among recipients of helical CT scans.
Before the new results, whether helical CT could save lives from lung cancer was widely debated, said Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society. But the new study—with its large, ethnically diverse group of subjects, and a design that randomly assigned patients to x-ray or spiral CT and followed their outcomes for several years—provides a clear snapshot of the possible benefits of spiral CT, at least in this group of people.
The research was conducted at 33 sites across the United States. The study began in 2002 and included more than 53,000 current or former heavy smokers aged 55 to 74. Study participants were randomly selected to be screened once a year for 3 years with either the low-dose helical CT scan or standard chest x-ray. They were followed for up to an additional 5 years, with researchers noting the outcomes of testing, any resulting diagnoses, medical follow-up, and deaths from lung cancer or other causes.
Those getting CT scans were 20% less likely to die of lung cancer during the study than those getting chest x-rays. Scientists estimated that for every 300 study participants screened with helical CT, one life was extended. The study also found that the death rate from any cause was 7% lower among the CT group, a finding that scientists say warrants further study. Lung cancer caused about one-quarter of all deaths in the trial.
Recommendations for screening still uncertain
However, more analysis of the study's findings will be needed before any recommendations about lung cancer screening can be made, Varmus and his colleagues pointed out.
Scientists said further data analysis could reveal a wealth of details about exactly who may benefit from the screening (by age, smoking history, gender and ethnicity, for instance), the impact of the testing on patients, and whether the CT scanning is most effective once every year, or every 2 years, or more.
The American Cancer Society will be promptly and carefully reviewing the study findings once they are published in full, and may issue recommendations about screening at that time.
Results may not apply to all smokers
Participants in the National Lung Screening Trial had no history or signs of lung cancer, and all had at least a 30 pack-year history of smoking (equivalent to smoking a pack a day for 30 years).
“It’s important to remember that this is the group that participated in this trial, and the results don’t necessarily apply to people who have not been heavy smokers for a long time now or in the past,” Lichtenfeld said, noting that people with a smoking history who might want to be screened should discuss the pros and cons of their individual situation with their health care providers. “For people who may have smoked a pack a day for 10 years and stopped, this study has no implication for them, and in fact the harms of the test could outweigh the benefits.”
Screening carries risks, too
Between 20% and 60% of screening CT scans of current and former smokers show suspicious masses or other abnormalities, research has shown. Most are not lung cancer—they can be areas of inflammation, scars from smoking or other noncancerous conditions. But these “false positive” findings nevertheless make patients more anxious and may require additional testing, including unnecessary biopsies or surgeries that carry their own risks, especially to patients who have other serious illnesses such as heart or lung disease.
Also, screening may detect small cancerous tumors that would never grow to be life-threatening but still would cause a patient to experience anxiety and unnecessary procedures or treatments.
In the current study, among patients undergoing CT scanning, the rate of false positives was about 25%, researchers said. Those data need to be evaluated further, said the NCI’s Richard Fagerstrom, lead statistician for the study, who noted that fewer false positives occurred among patients receiving helical CT screening than chest x-rays.
CT scans also expose people to radiation. The radiation dose from the CT scanning in the trial is generally considered less than what a person might receive from non-medical background radiation sources in one year, and was approximately 20% of the dose of a conventional diagnostic CT scan, said UCLA radiologist Denise Aberle, national principal Investigator for the new trial. But the excess radiation is still a factor that needs to be considered.
Screening CTs are not generally covered by insurance at this time.
Tobacco control efforts still crucial
Lung cancer accounts for about 15% of all U.S. cancer cases, and about 28% of cancer deaths. An estimated 222,520 diagnoses, and 157,300 deaths, from lung cancer are expected in the United States in 2010. “Over 85% of those victims are present or former smokers,” Dr. Varmus said.
Smoking is by far the most significant risk factor for lung cancer. About 20% of U.S. adults, or 46.6 million people, smoked in 2009, according to the Centers for Disease Control and Prevention.
"No one should come away from this believing it's now safe to continue to smoke or to start smoking," Varmus noted. "This screening does not protect the large majority of subjects from death from lung cancer."
It’s also important that the public understand that much work needs to be done to prevent lung cancer and improve survival in people who develop the disease.
“We still have to recognize that many lives are not saved,” Dr. Lichtenfeld said. “For people who are smoking—they should stop. For people who aren’t smoking—they shouldn’t start. And for people whose lives may not be saved by screening, we have to have better treatments that are effective in saving more lives.”
The National Lung Screening Trial was supported by the National Cancer Institute at a cost of more than $250 milliion, Varmus said.
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