Study examines use of Lung-RADS categories during follow-up CT screening

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Application of the Lung-RADS classification in clinical practice had excellent diagnostic performance in detecting cancer during follow-up CT examinations, but strict application led to the downgrading of some malignancies, according to a new study.

The retrospective study, published in the American Journal of Radiology, included 185 patients who underwent lung cancer screening CT examinations between July 2015 and August 2018. The clinical application of the Lung-RADS classification identified 50 category 2 nodules, 45 category 3 nodules, 47 category 4A, 30 category 4B nodules and 13 category 4X nodules.

The study authors noted that strict application of the Lung-RADS classification resulted in category changes for 59 of the 185 nodules. These category changes were due to a new solid nodule less than 4 mm, a ground-glass nodule less than 30 mm, or nodule size unchanged since the last examination, according to the study. With category adjustments, researchers noted that strict application of Lung-RADS led to 83 nodules being Category 2, compared to 50 nodules identified as Category 2 via clinical application of Lung-RADS. The study authors found that none of the 50 clinical Lung-RADS grade 2 nodules were cancerous while seven of the 83 nodules reclassified to grade 2 via strict Lung-RADS were found to be cancerous.

The subjective interpretation of the Lung-RADS guidelines in clinical practice surprised Mark M. Hammer, MD, study co-author and assistant professor at Harvard Medical School.

“(We found that) radiologists often deviate from strict application of Lung-RADS guidelines to lung nodules in screening for lung cancer. However, they were actually more successful in detecting cancers,” noted Dr. Hammer, a chest radiologist affiliated with Brigham and Women’s Hospital in Boston.

“The main reason for this is that about a quarter of the lung cancers in our study progressed so slowly that they remained unchanged over a short follow-up interval. Lung-RADS designates these as category 2 (“benign”) , which would have led to more complacency about these nodules.But in clinical practice, radiologists upgraded these nodules to higher categories, reflecting the true risk of malignancy.

For existing nodules, clinical application of Lung-RADS had sensitivity and specificity of 100% and 94%, compared to 65% and 98% for strict Lung-RADS, according to the study. The study authors also noted that the clinical Lung-RADS had an area under the curve (AUC) for cancer of 0.96 compared to 0.81 for the strict Lung-RADS. For newly detected nodules, researchers reported that clinical Lung-RADS had a sensitivity and specificity of 100% and 41%, compared to 74% and 38% for strict Lung-RADS. The study authors noted that the optimal diameter threshold was 8 mm for existing nodules and 6 mm for new nodules.

Limitations of the study, according to the study authors, included a retrospective analysis, small sample size, and being conducted within a single healthcare network.

While acknowledging that there is still much to learn about the treatment of slow-growing lung cancers, Dr. Hammer said, “Radiologists should feel free to use higher Lung-RADS categories (probably 4X) to nodules that are unchanged but still likely to be lung cancers based on their appearance.

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