New research finds that the Lung-RADS framework used to categorize nodules seen on lung cancer screening is useful but should be routinely re-evaluated, and future Lung-RADS iterations should consider these findings from real-world practice to improve the system's clinical utility.
Lung-RADS is a quality assurance tool "designed to standardize lung cancer screening CT reporting and management recommendations, reduce confusion in lung cancer screening CT interpretations, and facilitate outcome monitoring," according to the American College of Radiology. The organization introduced the system "to standardize reporting and management of nodules," noted Dexter Mendoza, MD, Assistant Professor of Diagnostic, Molecular, and Interventional Radiology at Mount Sinai, and lead author of this study.
"It was retrospectively applied and validated on clinical trial data, but its effectiveness in routine clinical practice has not been validated," said Mendoza, who was a radiologist at Massachusetts General Hospital (MGH) at the time the research was conducted.
With this study, which was published online in the American Journal of Roentgenology (2022; https://doi.org/10.2214/AJR.21.27180), Mendoza and his co-authors sought to see if Lung-RADS "performed well in our lung cancer screening program patients at MGH. And it does," he stated. "In fact, we found that nodules we categorized lung-RADS 3 or 4 had a relatively high likelihood of turning out to be malignant-higher than previously reported and estimated. This proves that Lung-RADS can be effective if used appropriately."
Lung-RADS classifications for lung cancer screenings with low-dose computed tomography fall into four categories: 1-2 constitute negative screening results, and categories 3 and 4 constitute positive results. As the authors noted, Lung-RADS category 3 and 4 nodules account for most cancers among screening-detected lung cancers and are considered actionable nodules with management implications. The cancer frequency among such nodules "is estimated in the Lung-RADS recommendations and has been investigated primarily using retrospectively assigned Lung-RADS classifications," the researchers wrote.
Mendoza and colleagues set out to assess the frequency of cancer among lung nodules assigned Lung-RADS category 3 and 4 at lung cancer screening in clinical practice, as well as evaluate the factors that affect the cancer frequency within each category.
Their retrospective study was based on the review of clinical radiology reports of 9,148 consecutive low-dose CT lung cancer screenings performed in nearly 5,000 patients between June 2014 and January 2021 as part of an established lung cancer screening program. Unique nodules assigned Lung-RADS category 3 or 4 that were clinically categorized as benign or malignant by a multidisciplinary conference, considering histologic analysis and follow-up imaging, were selected for further analysis. Benign diagnoses based on stability required at least 12 months of follow-up imaging. Indeterminate nodules were excluded. Cancer frequencies were evaluated.
Among the 9,148 lung cancer screening examinations, 857 were assigned Lung-RADS category 3, and 721 were assigned category 4. The final analysis included 1,297 nodules in 1,139 patients. A total of 1,108/1,297 nodules were deemed benign, with 189/1,297 categorized as malignant. Frequencies of malignancy for category 3, 4A, 4B, and 4X nodules were 3.9 percent, 15.5 percent, 36.3 percent, and 76.8 percent, respectively. A total of 45/46 endobronchial nodules (all category 4A) were deemed benign based on resolution. Cancer frequency was 13.1 percent, 24.4 percent, and 13.5 percent for solid, part-solid, and ground-glass nodules, respectively.
When applying Lung-RADS for lung cancer screening clinical practice, "the frequency of Lung-RADS category 3 and 4 nodules, as well as cancer frequency in these categories, were higher than prevalence and cancer risk estimated for category 3 and 4 nodules in the Lung-RADS recommendations and reported in earlier studies using retrospective category assignments," the authors wrote, adding that "nearly all endobronchial category 4A nodules were benign."
The researchers ultimately found that, while the Lung-RADS framework for categorizing nodules found on lung cancer screening is useful, it should be regularly re-evaluated. Mendoza attributes this to the finding that reported endobronchial nodules "overwhelmingly resolved and were in fact just endobronchial mucus/debris. Only one out of reported 46 turned out to be cancer."
Currently, Lung-RADS categorizes these endobronchial nodules as category 4A ("suspicious") regardless of size, noted Mendoza, adding that future versions of Lung-RADS should take this study's findings into consideration to continue enhancing the framework's clinical usefulness.
"We believe future iterations of Lung-RADS can either re-categorize these to a lower category or set size thresholds on what endobronchial nodules should be categorized as 4A. But this is based on findings from only one institution. I would be interested to see if the same holds true for other lung cancer screening programs."
For the radiology suite, the key takeaway from these findings is for radiologists to familiarize themselves with Lung-RADS "and use it accordingly in reporting lung cancer screening examinations," Mendoza stated. "We also encourage groups and institutions to regularly evaluate their [lung cancer screening] program outcomes to see if there is room for improvement with respect to reporting these exams and managing screening patients."
Mark McGraw is a contributing writer.