High Rate of False-positive Results in Lung Cancer Screening with CT Scan

Posted on April 29th, 2010 by

Screening for lung cancer using computed tomography (CT) scans can yield a high rate of false-positive results, according to a study published in the Annals of Internal Medicine. False-positive results are risky because they may lead to invasive follow-up testing, financial burden, and anxiety.

CT scanning is being studied as a screening tool for lung cancer. Several studies have indicated that screening with CT scan appears to provide improved long-term survival for patients with lung cancer; however, not all results from these studies demonstrate improved survival, which is why the medical community has not adopted CT scanning for standard screening for lung cancer.

In order for new screening methods to be adopted into routine clinical care, the measures must identify cancer early enough to improve outcomes, must be economically feasible, and must detect cancer with an acceptable degree of accuracy. As well, in order to encourage patient compliance, screening measures must not be too invasive, painful, or risky. To date no screening measures for lung cancer have been identified that provide a confirmed benefit.

To estimate the frequency of false-positive test results among patients undergoing screening for lung cancer using CT scans, researchers evaluated approximately 3,000 individuals. Study participants were current of former smokers who had never been diagnosed with lung cancer. They underwent screening with CT scan or chest X-ray at the beginning of the study and again one year later. Patients were then followed for 12 months to determine if positive screening results were valid or false-positive (meaning further diagnostic testing did not find lung cancer).

  • Following the first screening, patients undergoing CT scan had a 21% probability of a false-positive result compared with 9% for those undergoing chest X-ray.
  • After two rounds of screening, the CT group had a 33% probability of a false-positive versus 15% for the chest X-ray group.
  • 7% of patients in the CT group receiving a false-positive result underwent a follow-up invasive diagnostic procedure compared with 4% in the chest X-ray group.

The researchers concluded that screening for lung cancer with CT scans carries a “substantial” risk for false-positive results. Because CT scans themselves may pose a risk to patients by exposing them to radiation (a potential risk for cancer), and false-positive results can lead to invasive procedures that are accompanied by economic and psychological burdens, further study of CT scans for lung cancer screening are needed before this method can be widely recommended.

Reference: Croswell JM, Kramer BS, Kreimer AR, et al. Cumulative incidence of false-positive results in repeated, multimodal cancer screening. Annals of Internal Medicine. 2009 May-Jun;7(3):212-22.

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