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False-Positive Test Results in a Study of Lung Cancer Screening FREE

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The summary below is from the full report titled “Cumulative Incidence of False-Positive Test Results in Lung Cancer Screening. A Randomized Trial.” It is in the 20 April 2010 issue of Annals of Internal Medicine (volume 152, pages 505-512). The authors are J.M. Croswell, S.G. Baker, P.M. Marcus, J.D. Clapp, and B.S. Kramer.

Ann Intern Med. 2010;152(8):I-40. doi:10.7326/0003-4819-152-8-201004200-00003
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What is the problem and what is known about it so far?

Lung cancer is the most common cause of cancer-related death among men and women in the United States. Lung cancer is difficult to treat unless it is found at very early stages. Unfortunately, most people do not develop symptoms until the cancer has spread. Symptoms include cough, spitting up blood, weight loss, and difficulty breathing. Tests that can detect lung cancer before patients have symptoms include chest x-rays and computed tomography (computerized x-rays, also called CT scans). Screening for lung cancer would involve using one of these tests to look for lung cancer in persons who have no symptoms. However, no studies to date have proven that screening helps people live longer. In addition, these tests expose patients to radiation and often have false-positive results. False-positive test results mean that the test shows an abnormality that turns out not to be cancer; such results can lead to unnecessary worry, testing, and surgery.

Why did the researchers do this particular study?

To find out the frequency of false-positive test results if persons participated in repeated rounds of lung cancer screening with chest x-ray or CT scan.

Who was studied?

3190 current or former smokers aged 55 to 74 years.

How was the study done?

The researchers assigned study participants at random to receive either chest x-ray or CT scan with repeated testing after 1 year if the first test result was normal. They followed patients with abnormal test results to see whether they were true-positive or false-positive results. They followed patients for 12 months after the final screening test to see who developed cancer.

What did the researchers find?

After 1 CT scan, the risk for a false-positive result was 21% for CT and 9% for chest x-ray. After 2 CT scans, these risks increased to 33% and 15%, respectively. Of the patients who had a false-positive CT scan, 7% had a resulting invasive procedure. Invasive procedures occurred in 4% of patients with a false-positive chest x-ray.

What were the limitations of the study?

Because patients had only 2 rounds of screening over 2 years, it would be expected that false-positive test results would increase with additional rounds of screening over long periods.

What are the implications of the study?

Even after only 2 screening examinations, false-positive test results are very common when chest x-ray or CT scans are used to screen smokers for lung cancer. False-positive test results are more frequent with CT scans than with chest x-rays. Frequent false-positive results may limit the usefulness of these tests for lung cancer screening, but more definitive studies of both the benefits and risks are ongoing.





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