Redefining a Positive CT Finding for Lung Cancer May Slash Radiation Risks and Unneeded Surgery

The findings were published February 19, 2013, in the journal Annals of Internal Medicine.

In CT screening for lung cancer, the positive result of the initial low-dose CT indicates whether further diagnostic work-up is needed before the first arranged repeated screening. Currently, the researchers’ threshold for defining a positive result is 5 mm. Employing a threshold of 7 mm or 8 mm to define a positive lung cancer result in a baseline round of CT could significantly decrease unnecessary workup of nodules that are not cancerous. However, additional future research is required to determine the extent to which increasing the threshold may postpone diagnosis of cancer in some patients.

“Over the past decade, due to advancements in CT technology and our increased knowledge, the frequency of identifying a noncalcified nodule [NCN] of any size on the initial baseline CT scan has almost tripled, said Claudia I. Henschke, PhD, MD, professor of radiology at the Icahn School of Medicine at Mount Sinai and I-ELCAP principal investigator. “Using too small of a measurement to define a positive result may cause excessive diagnostic work-up and unnecessary treatment, while using too large of a measurement may delay diagnosis. We feel that nodule size, including volume, remains the most useful and reproducible metric of the most benefit to our patient population. Just as the definition of a positive result has been revised in the past to reflect updated data, we feel it is again time to use the information at our disposal to create a more restrictive definition.”

Researchers reviewed medical records for a cohort of 21,136 patients who had a baseline CT conducted between 2006 and 2010 to evaluate how using a more restrictive threshold in the baseline round of screening would affect the number of positive findings and delayed diagnoses. Of the study participants undergoing baseline screenings, 57% had at least one NCN discovered. Using the current designation of 5 mm, 16% (3,396 of the 21,136 patients) had a positive result of the baseline screening. Among those whose largest nodule was between 5–9 mm, eight were detected with lung cancer within 12 months of baseline enrollment. Increasing the threshold to 6, 7, 8, and 9 mm would have lowered the frequency to 10%, 7%, 5%, and 4%, respectively, therefore decreasing additional work-up by 36%, 56%, 68%, and 75%, respectively.

“Changing the size threshold for a positive screening could help reduce the harms associated with unnecessary work-up,” said Dr. Henschke. “I can’t say with certainty what the best definition of a positive result is, but our data provide the basis for contemplation and reevaluation.”

I-ELCAP is an international collaborative group of more than 60 participating institutes comprised of specialists on lung cancer-related disorders. Earlier studies from the group revealed that lung cancers identified through CT screening have an 80% estimated cure rate compared to a 10% cure rate for lung cancers detected in the clinical setting in the absence of screening.

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Icahn School of Medicine at Mount Sinai