Low-dose computerized tomography -- or CT -- scans better detect earlier stages of lung cancer than a standard chest X-ray, significantly cutting deaths from the disease, the National Cancer Institute announced today.
The NCI's study enrolled 53,000 current and past smokers who were screened annually for three years by either CT scan or conventional chest X-rays and found those who were screened CT were 20 percent less likely to die from lung cancer.
In a teleconference today, trial investigators said they presumed CT scans were able to detect smaller tumors, which led to an earlier diagnosis and subsequently earlier intervention.
"This has the potential to save many lives among those at risk for lung cancer," said Dr. Harold E. Varmus, director of the National Cancer Institute, at the teleconference.
The trial, which began in 2002, ended earlier than expected after the Data Safety Monitoring Board, an independent panel of reviewers, found there was sufficient data collected to show a significant decrease in lung cancer death in participants who underwent CT screening.
Lung cancer is the major cause of death from all cancers in United States, said Varmus. It will cause 157,000 deaths in U.S. this year, he said.
A CT scan uses multiple X-ray views to assemble cross-sectional images of structures inside the body. Because its use involves several X-ray scans, it generally exposes patients to nearly three times the degree of radiation than a single X-ray.
Still, investigators said the amount of radiation in a low-dose scan such as the one used is almost equivalent to a standard mammography, which is used to detect breast cancer.
CT Scans Also Pose Disadvantages, Experts Say
Despite seemingly positive results, investigators at the teleconference said CT scans also pose many hurdles. According to Dr. Douglas Lowy, laboratory chief and principal investigator at the National Cancer Institute, while a CT may detect a tumor earlier, more tests will be needed to track the tumor and treat if necessary.
"Subsequent procedures are always needed to evaluate for a diagnosis," which can include follow up scans, biopsies, and surgery to remove potentially cancerous tumors, said Lowy.
And while Varmus noted CT scans may be better able to detect smaller tumors, it's likely the tumors would not have grown to be cancerous.
"Simply identifying a tumor at an early stage is not saying that CT is an effective modality," said Varmus.
Scan results that show tumors may lead experts to mistakenly detect lung cancer, he said.
However, according to Dr. Claudia Henschke, professor of radiology and chief of the Chest Imaging Division of the Weill-Cornell Medical Center at New York-Presbyterian Hospital, many experts can avoid over-diagnosing and over-treating patients by using the scan to monitor tumors over time.
"Every year after you calculate how fast the tumor is growing," said Henschke.
For now patients would bear the cost for screening. CT scans, which cost about $300, are covered by some insurance companies to diagnose cancers. But insurance companies do not cover scans as a method to screen for the disease.
However, according to Henschke, early detection of tumors through CT scans -- which can lead to earlier diagnosis and treatment of lung cancer -- is worth the price.
"Late-staged treatment is more costly than early-stage treatment," said Henschke, whose initial 1999 study published in Lancet showed that CT scans were more effective than chest x-rays to pick up earlier-stage lung cancers. Henschke was not involved in the latest NCI trial.
CT Screening Not for Everyone
While the latest trial showed that CT scans screening decreased the number of people who died from lung cancer, Varmus said CT scans should not be used to prevent the disease among the general population.
The results of the study only applied to heavy current and previous smokers deemed at higher risk for lung cancer. The best way to prevent the disease, he said, is to stop smoking.
According to Dr. Joseph Bokar, medical oncologist at University Hospitals Case Medical Center in Cleveland, Ohio, quitting smoking is "more effective than any screening program."
In fact, not all folks who are at high risk for lung cancer should ask for CT scans, according to Dr. Len Lichtenfeld, deputy chief medical officer at the American Cancer Society. Screening may not be appropriate for those who suffer from later-stage lung or heart disease, he said.
"Ask yourself the question, if you find an abnormality, are you in good enough condition to go through the surgery or the treatment that follows," said Lichtenfeld.
And questions still remain on how best to implement CT scans as a screening tool for lung cancer. Although many studies suggest x-ray does not prevent lung cancer death, Lichtenfeld said only individual doctors can evaluate the best screening method for each patient.
"What was not said today is that we have enough to make a blanket recommendation that everyone get screened [by CT scans]," said Lichtenfeld. "It's going to take time for experts to give it some thought."
"For all this we really need to develop guidelines," said Henchke.
Investigators said they plan to publish full review of their results in subsequent months.
"All of these considerations have implications for recommendations," said Lowy. "Further analysis will be needed before concluding broader use for this method."