Researchers from the National Institutes of Health have reported that individuals who undergo lung cancer screening with low-dose computed tomography (LDCT) are at a high risk for receiving false-positive results. The details of this study were presented at the 2009 annual meeting of the American Society of Clinical Oncology in Orlando, Florida, on May 30.[1]

Lung cancer is the most common cancer in the world and is the leading cause of cancer death, with 160,000 deaths in the United States annually. No screening procedure for lung cancer has been proven to decrease the number of lung cancer deaths, and there is currently no consensus as to the best way to screen for lung cancer. Historically, physicians have used imaging tests (such as LDCT and chest X-ray) and sputum cytology to detect lung cancer. New screening procedures continue to be evaluated and refined.

Researchers from the National Institutes of Health conducted a study that involved 1,610 patients who underwent screening with LDCT and 1,580 who underwent screening with chest X-ray. All participants in the study were current or former smokers between the ages of 55 and 74. All subjects underwent baseline screening followed by another screening exam one year later. They were then followed for an additional year.

A positive screen was defined as any noncalcified nodule greater than 4 millimeters or any other radiographic finding deemed suspicious for cancer. A false-positive was defined as a positive screen that was then followed by a completed negative work-up or 12 or more months of follow-up with no cancer diagnosis. After analyzing the screening results, the researchers then quantified the cumulative risk of receiving a false-positive result from lung cancer screening. In the LDCT group, the risk of a false-positive result was 21% after one scan and 33% after the second. In the chest X-ray group, the risk of a false-positive result was 9% after one X-ray and 15% after the second.

The researchers concluded that there is a significant risk of receiving a false-positive result with LDCT screening and this could result in a potential economic burden on the system as well as cause unnecessary stress among individuals being screened.

Comments: No medical organization currently recommends the routine use of CT screening for individuals at high risk of developing lung cancer. However, there is a growing body of data that suggests CT screening detects early lung cancers that are potentially curable. The only down-sides to CT screening are the expense and exposure to excessive radiation. Expenses of CT screening are not limited to the direct cost of CT screening but involve the cost of investigating many benign nodules that are detected.  However, individuals at high risk for developing lung cancer should be allowed to decide for themselves whether or not they wish to undergo CT screening after all the facts are presented to them. Many high-risk individuals have already chosen to undergo annual CT screening at their own expense in the absence of available studies to participate in.

Reference:

[1] Crosswell JM, Baker SG, Marcus PM, et al. Cumulative risk for a false-positive test using low-dose computed tomography in lung cancer screening. Journal of Clinical Oncology. 2009;27:15s Abstract CRA1502.