Clinicians have pinpointed the optimal threshold at which a small growing lung nodule should be referred for further investigation.

In a bid to find a balance between reducing unnecessary referrals while facilitating early cancer diagnoses, researchers analysed outcomes for SUMMIT study participants with nodules of ≥80 mm³ and <300 mm³ on baseline scan, who then underwent an interval scan three months later.

Published in Thorax, results showed that the risk of malignancy was more than four times higher in growing solid nodules greater than 200 mm³ after three months compared to those 200 mm³ or under (58.3% versus 13.3%).

Nodules found to be stable after three months were scheduled for additional scans at one and two years, while those showing growth and with a of volume >200 mm³ were referred to an MDT for assessment and those showing growth with a volume less than this were scheduled for a further scan three months later.

Based on the data, the researchers, led by Dr Andrew Creamer, a clinical researcher at University College London,  calculated the predictive value of a combination of nodule growth (change of ≥25%) and size >200 mm³ to be 65.9% at a cancer-per-nodule or 60.5% on a cancer-per-participant basis.

“Our results provide support for a conservative approach involving close CT observation in growing nodules ≤200 mm³. Of the nodules in this category that were malignant, all but one remained at stage I, with an overall false-negative rate of  1.9%,” the investigators noted.

“Importantly, this approach avoids unnecessary MDT referral and further investigation for a finding which is benign or indolent in 86% of cases”.

A key limitation of the study is that only nodules “with reliable segmentation at follow-up scan” were included in the evaluation, so a small number where reliable volumetric analysis was not possible were excluded. “This may limit generalisability in contexts where nodule volumetry is not routinely available or for nodules where volume cannot be accurately assessed,” the researchers said.

Nevertheless, the findings indicate that “a solid nodule management protocol encompassing a combination of growth and minimum size threshold is safe and reduces unnecessary MDT referrals for benign lesions, while maintaining early-stage lung cancer diagnosis,” they concluded.