Spiral CT Scans for Lung Cancer Screening

National Cancer Institute
Friday, 7 July 2000

Lung cancer, which is most frequently caused by cigarette smoking, is the leading cause of cancer-related death in the United States, claiming almost 157,000 lives in 2000. Spiral computed tomography (CT or CAT) scans are being advertised as a new way to find early lung cancer in smokers and former smokers. However, questions about the technology's risks and benefits remain unanswered.

Promising evidence from several studies shows that the scans can detect small lung cancers. But detecting these early tumors has not been proven to reduce the likelihood of dying from lung cancer, the gold standard for any cancer screening test. The National Cancer Institute (NCI) is designing a large study that should conclusively answer whether spiral CT does in fact reduce mortality.

While spiral CT scans may eventually prove to be an effective lung cancer screening tool, they can trigger unnecessary invasive testing or even chest surgery. Scarring from smoking and other non-cancerous changes in the lungs can mimic tumors on CT scans, challenging the radiologists who read them. Interpretations of the scans can vary, leading to confusion about recommendations for follow-up care.

About 20 percent to 40 percent of CT scans of smokers and former smokers will show abnormalities that are not cancer. When these suspicious areas, or nodules, are found, the physician may recommend waiting several months to a year before a repeat scan, to see if the nodule has grown.

The physician may also advise an immediate lung biopsy, a potentially risky procedure that involves the removal of a small amount of tissue, either through a scope fed down the windpipe (bronchoscopy) or with a needle through the rib cage (CT-directed needle biopsy). Possible complications from biopsies include partial collapse of the lung, bleeding, infection, and pain and discomfort.

Depending on the size and location of the nodule, chest surgery (thoracotomy) to obtain a larger biopsy may be recommended. Thoracotomy is a major surgery that removes substantial amounts of lung tissue; the procedure can damage nerves in the chest and may lead to chronic pain.

More than half of the hospitals in the United States own a spiral CT machine. These machines are routinely used for staging lung and other cancers – that is, determining how advanced the cancer is after diagnosis. But recently, some hospitals have begun promoting spiral CT scans to smokers for early detection of lung cancer, despite the lack of solid evidence. Each scan costs $300 to $1,000.

Some experts worry that this marketing may lull smokers into falsely believing that they can continue smoking without increasing their risk of dying from lung cancer. But the only proven way to reduce the risk of lung cancer is not to smoke (85 percent of all lung cancers are caused by smoking). For people who do smoke, quitting reduces the risk of lung cancer considerably over the course of several years.

The NCI study will track tens of thousands of smokers and former smokers to see if those who are screened with spiral CT scans have a lower mortality rate than those who do not undergo the scans. Research has shown that high-risk individuals say they would be willing to participate in the study, even if they were selected to receive another intervention instead of spiral CT.

A preliminary study is being done prior to the large-scale study in which about 3,000 smokers will be recruited over several months to receive either a CT scan or a chest X-ray. This preliminary study will provide important information on how much follow-up (additional scans, biopsies, surgery, etc ) is needed after each type of lung cancer screening. In addition, this short-term study will see whether the stated willingness of high-risk people to participate in such a trial will translate into actual participation. Medical centers that are part of the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial will begin this study in September 2000.

The PLCO is also separately examining whether annual chest X-rays, which are easier to perform than spiral CT scans, can reduce mortality from lung cancer. The PLCO trial began in 1994 and is following nearly 150,000 men and women. People participating in the PLCO Cancer Screening Trial cannot participate in the Spiral CT special study.

How it works: Spiral CT uses X-rays to scan the entire chest quickly, in 15 to 20 seconds, during a single breath-hold. Throughout the procedure, the patient lies very still on a table. The patient passes through the X-ray machine, which is shaped like a doughnut with a large hole. The machine rotates around the patient and a computer creates images from the scan, which can be reconstructed into a three-dimensional model of the lungs.

For more information, or to contact National Cancer Institute, see their website at: www.cancer.gov