Although interstitial lung abnormalities (ILA) are commonly identified in lung cancer screenings, the long-term prognosis of their presence is not definitively known. However, studies have shown that identification of ILA during a screening increases the eventual diagnosis of interstitial lung disease (ILD) by up to five times.

Of the three categories of ILAs—non-subpleural nonfibrotic, subpleural nonfibrotic, and subpleural fibrotic—studies have shown that subpleural fibrotic ILA (Figure) is the most likely of these parenchymal lung changes to progress. Traction bronchiectasis is a primary characteristic of subpleural fibrotic ILA and has been distinguished as a significant predictor of poor prognosis.

Conal Hayton, PhD, and colleagues sought to examine patients with ILA identified via CT scan to determine subsequent outcomes, including ILD diagnosis, progression-free survival, and mortality. Participants included 1,384 individuals who received a lung cancer screening via CT scan. Of them, 54 were shown to have ILAs, among whom 22 eventually received a diagnosis of ILD. Patient-reported outcome measures were compared among the participant group with identified ILA and the participant group with diagnosed ILD.

Dr. Hayton discussed the findings of this work with Physician’s Weekly.

PW: Why did this topic need exploration?

Dr. Hayton: Lung cancer screening has been hugely successful at identifying early-stage lung cancers; however, ILAs are nearly twice as common on screening CT scans as lung cancer. Evidence to date suggests that the presence of ILAs is associated with poor outcomes, including a nearly three times increased risk for mortality; however, it is unclear what proportion of ILA picked up on screening go on to be diagnosed with ILD. We felt it was important to explore outcomes in individuals picked up with ILA on screening to understand the natural history of these changes, identify risk factors for progression, and help determine how these individuals should be followed-up.

What are the most important findings from your study for physicians to understand?

In this study, we identified 4% ILA in a lung cancer screening cohort; 37% had radiologic progression of ILA at 1 year and 40% were diagnosed with ILD within 5 years. Fibrotic ILA, defined by the presence of traction bronchiectasis, was a strong predictor of mortality, reduced progression-free survival, and diagnosis of ILD.

How can these findings be incorporated into practice?

It is important not to ignore ILA picked up on lung cancer screening CTs, as 40% will go on to be diagnosed with ILD. The presence of traction bronchiectasis was the strongest prognostic indicator, which is consistent with previous studies. Consideration of following-up with individuals with fibrotic ILA would be recommended as a minimum in individuals identified with ILA on lung cancer screening.

What would you like to see in future research?

Future research should focus on the identification of biomarkers that could help predict progressive disease in ILA. Management of ILA picked up at screening will involve a risk stratification model combining risk factors, like those picked up in our study and other retrospective work, and biomarkers that can predict progression. This will allow us to identify those at the highest risk for progression and target follow-up and treatment to those groups.