Increasing nodule size threshold in a CT lung scan reduces false positives

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Increasing the nodule size threshold when screening patients for lung cancer with computed tomography could result in fewer false-positive results, according to a study published in the Feb. 19 issue of the Annals of Internal Medicine.

The current threshold for defining a positive result in CT screening for lung cancer is 5 mm. In this study, researchers, led by Claudia I. Henschke, Ph.D., M.D., from the Mount Sinai School of Medicine in New York, increased the threshold to determine to what extent that would decrease the unnecessary workup of nodules that aren't malignant.

The researchers prospectively evaluated the records of 21,136 patients who had a baseline CT performed between 2006 and 2010. Using the current definition of 5 mm, 16 percent had a positive result with the baseline screening. Increasing the threshold to 6, 7, 8, and 9 mm would have lowered the frequency of positive results to 10.2, 7.1, 5.1, and 4.0 percent respectively, thus decreasing further work-up by 36, 56, 68, and 75 percent respectively.

At the same time, the researchers determined that increasing the threshold size would delay a lung diagnosis by, at most, nine months.

"Of course, to delay any diagnosis in lung cancer is significant, but those cancers that were found because of the workup still needed one or two CT scans to determine that they were really cancers," Henschke said, according to an article in Medscape Medical News. "All of them were still in stage I when they were diagnosed."

Henschke, in an announcement accompanying the study, added that changing the size threshold for a positive screening could help reduce harms linked with unnecessary work-up. "I can't say with certainty what the best definition of a positive result is, but our data provide the basis for contemplation and re-evaluation," he said.

To learn more:
- see the study abstract
- see the article in Medscape Medical News
- read the announcement

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