With increasing life expectancy and wider use of chest computed tomography (CT), interstitial lung diseases (ILD) is being encountered more frequently in clinical practice. Accordingly, ILD has become an increasingly important concern for physicians. Since the launch of Korea’s national lung cancer screening program in 2019, the number of low-dose chest CT scans has increased substantially. This change has led to the more frequent detection of early, mild interstitial lung abnormalities (ILAs) that previously may have gone unnoticed. The clinical spectrum of ILD and interest in its treatment have also expanded considerably, ranging from early findings such as ILA to idiopathic pulmonary fibrosis (IPF), progressive pulmonary fibrosis (PPF), and emerging forms of drug-induced interstitial lung diseases (DILD) associated with newer medications.

Whereas earlier ILD care focused primarily on diagnosis and prognostic evaluation in pulmonary fibrosis, recent care has shifted toward ILA risk assessment, early recognition of PPF, and precision-medicine approaches based on imaging, genetic, and serum biomarkers [1,2]. This shift has been driven by the introduction of antifibrotic agents and the expansion of newer anticancer therapies, including immune checkpoint inhibitors and antibody-drug conjugates (ADCs). These developments have shifted clinical attention from diagnosis alone toward long-term ILD management [3,4].

This special issue of the Journal of the Korean Medical Association, titled “Interstitial Lung Diseases in Clinical Practice: from Incidental Interstitial Abnormalities on Computed Tomography to Updated Treatment Strategies for Interstitial Lung Diseases,” guides readers through these recent changes in ILD classification, detection, and treatment. The issue includes four review articles intended to provide practical clinical guidance for frontline physicians.

The first article defines ILA, describes its classification and prevalence, and explains its clinical importance. ILA is often detected incidentally on chest CT scans performed for lung cancer screening or other indications in individuals without ILD-related symptoms [5].

Previously, ILA was often regarded as an age-related change or an indeterminate imaging finding. However, large recent studies have shown that ILA is associated with worse lung function, more respiratory symptoms, higher mortality, and increased lung cancer risk. Fibrotic ILA can progress to IPF and has been associated with biomarkers such as the MUC5B gene, Krebs von den Lungen-6, and telomere length. Recent statements from the American Thoracic Society (ATS) and the Fleischner Society describe ILA as part of an early ILD spectrum rather than an incidental imaging finding without clinical relevance. Accordingly, high-risk individuals should undergo regular follow-up, including CT every 12–24 months and pulmonary function testing every 6–12 months [1,2].

The second article builds on this foundation by reviewing the modern classification system and practical diagnostic strategies for ILD, which encompasses more than 200 heterogeneous parenchymal lung diseases [6]. Centered on the 2025 revision by the European Respiratory Society (ERS) and ATS, the article presents ILD classification as a multi-axial concept that incorporates etiology, morphologic pattern, disease behavior, and fibrotic status rather than relying on a simple cause-based framework [7]. It summarizes recent classification concepts related to PPF, interstitial pneumonia with autoimmune features, and exposure-related ILD and presents an integrated stepwise diagnostic algorithm. This approach reflects the recognition that, even when imaging patterns are similar, treatment response and prognosis can vary substantially according to the underlying cause. The concept of PPF also emphasizes that IPF is not the only progressive fibrotic disease. Since the INBUILD trial, the role of antifibrotic therapy has expanded to include various non-IPF fibrotic ILDs [8], reflecting a shift in ILD care from pathology-based diagnosis toward disease-behavior-based management. In addition, the article emphasizes the need for multidisciplinary discussion to improve diagnostic confidence, given that no single test is sufficient to diagnose ILD, and explains how prognosis and treatment response can differ substantially according to cause and clinical course, even among patients with identical morphologic patterns.

The third article explains the current criteria for diagnosing and treating IPF, the ILD subtype with the poorest prognosis [9]. It describes how the usual interstitial pneumonia (UIP) pattern on high-resolution CT is classified into four categories: UIP, probable UIP, indeterminate for UIP, and alternative diagnosis. IPF can be diagnosed on the basis of imaging findings alone when a UIP or probable UIP pattern is present, without the need for lung biopsy [3,4]. For treatment, the article recommends antifibrotic therapy with pirfenidone or nintedanib, which are effective antifibrotic agents [10,11]. Drug selection should also consider insurance coverage and adverse-effect profiles. The article introduces potential new treatments, including the selective phosphodiesterase 4B inhibitor nerandomilast, which has slowed forced vital capacity decline in recent trials. Nonpharmacologic treatments, including pulmonary rehabilitation, oxygen therapy, palliative care, and timely lung transplant evaluation, are also important components of comprehensive care.

The fourth article broadens the discussion to DILD, whose clinical importance has increased rapidly with the emergence of various new therapeutic agents for other diseases [12]. In particular, the expanded use of newer anticancer drugs—including ADCs such as trastuzumab deruxtecan (T-DXd), third-generation epidermal growth factor receptor inhibitors such as osimertinib and lazertinib, immune checkpoint inhibitors, and cyclin-dependent kinase 4/6 inhibitors—has substantially changed the epidemiology and clinical manifestations of DILD [13–15]. The 2025 ERS/ATS classification revision explicitly includes DILD in the interstitial pneumonia classification system, adds a new bronchiolocentric interstitial pneumonia pattern, and renames the diffuse alveolar damage (DAD) pattern; these are major classification changes. Of note, T-DXd-related DILD has emerged as a significant clinical issue, with some patients progressing to fatal DAD patterns; therefore, early detection and prompt drug discontinuation are critical. Furthermore, the potential role of nintedanib in some cases of progressive fibrotic DILD suggests that DILD management is evolving beyond inflammation suppression alone and toward selected antifibrotic strategies.

The four articles in this special issue are significant because they present the clinical course of ILD as a continuum, from incidentally detected ILA on CT to confirmed pulmonary fibrosis and treatment. In particular, the first article demonstrates that ILA is more than a simple radiologic abnormality; it may represent a precursor stage of IPF and other forms of PPF, and systematic classification with risk-based follow-up according to subtype may be important for long-term prognosis [5]. As Korea entered a super-aged society in 2024, the frequency of ILA detection is expected to increase. Therefore, incidentally detected ILA on low-dose chest CT should not be dismissed as an age-related change; instead, individualized follow-up strategies should be established alongside risk-factor assessment. Compared with Western cohorts, Koreans have a lower allele frequency of the MUC5B promoter variant and an ILA prevalence of approximately 3%, less than half that reported in Western populations. These epidemiologic and genetic differences support the need for management guidelines that reflect the characteristics of the Korean population.

From a diagnostic perspective, a multidisciplinary approach and the use of diagnostic-confidence concepts can reduce unnecessary invasive procedures and underdiagnosis, thereby supporting more appropriate treatment selection for individual patients [2]. The 2025 ERS/ATS classification revision addresses limitations of previous classifications that were confined largely to idiopathic interstitial pneumonias by integrating autoimmune-associated ILD, exposure-related ILD, and DILD into a unified system. This evolution is expected to improve clinical communication and research consistency. Furthermore, the practical approach of combining morphologic pattern-based and etiology-based classifications reflects clinical reality, in which prognosis and treatment response may differ by cause, even with the same UIP pattern. The establishment of the PPF concept provides a clinical basis for applying antifibrotic therapy to various fibrotic ILDs beyond IPF and has substantial clinical implications. Thus, the evolution of ILD classification systems functions not merely as academic refinement but as a practical framework directly linked to treatment decisions.

Advances in antifibrotic therapy have slowed lung function decline in patients with IPF, and accumulating clinical evidence suggests potential reductions in acute exacerbations and hospitalization risk [3]. In Korea, where insurance coverage is limited, drug selection should consider cost-effectiveness and adverse-effect profiles, and treatment adherence should be supported through adverse-effect management and patient education. Regarding DILD, the rapid expansion of newer anticancer drugs, particularly ADCs, has led to T-DXd-related DILD incidence rates of up to 28% in clinical trials; therefore, careful evaluation of ILA or baseline ILD on chest CT before anticancer therapy and active monitoring for respiratory symptoms during treatment are essential for patient safety [4]. These clinical challenges require close multidisciplinary collaboration among pulmonologists, radiologists, pathologists, and oncologists. Future research priorities include accumulating epidemiologic data in Koreans, applying artificial intelligence (AI)-based imaging analysis in clinical settings, and systematically analyzing domestic pharmacovigilance data related to DILD.

The four articles in this special issue provide a comprehensive and clinically practical overview of the ILD spectrum, offering substantive guidance for a broad readership ranging from primary care physicians to specialists. Systematic risk-based follow-up of incidentally detected ILA on CT, accurate ILD classification for treatment selection, and continued vigilance for DILD during the use of newer anticancer drugs will be essential clinical competencies for respiratory physicians in an aging society. As the burden of ILD increases, this special issue is expected to strengthen diagnostic and therapeutic capacity in frontline clinical practice and advance ILD research in Korea.