Drug-induced interstitial lung disease (DI-ILD) remains one of the most serious pulmonary toxicities associated with modern cancer therapies [1]. Although awareness of this complication has increased, timely diagnosis remains a significant clinical challenge. Early symptoms are often subtle and non-specific, making it difficult to distinguish DI-ILD from infection, cancer progression or other respiratory conditions. As a result, many patients are only diagnosed after significant lung injury has already occurred, when treatment options may be more limited and patient outcomes are poorer.

Earlier recognition of respiratory changes has the potential to alter this trajectory by enabling prompt investigation, appropriate treatment interruption where necessary, and timely initiation of corticosteroid therapy before irreversible lung damage develops [2,3]. In this blog, we explore why diagnosis is often delayed, the impact this can have on patient outcomes, and how emerging monitoring approaches could help to support a more proactive model of care.

Challenges in Diagnosing DI-ILD

Diagnosing DI-ILD typically requires a combination of clinical assessment, detailed medication history, high-resolution computed tomography (HRCT), pulmonary function tests (PFTs), and the exclusion of alternative causes such as infection or disease progression [1]. In some cases, bronchoscopy with bronchoalveolar lavage (BAL) or a surgical lung biopsy (SLB) may also be required [1].

Recognition of DI-ILD is particularly challenging in patients receiving cancer therapy, as symptoms often overlap with other common conditions such as respiratory infections, asthma, chronic obstructive pulmonary disease (COPD), and cancer progression. Consequently, DI-ILD may be attributed to other causes, which can lead to delays in diagnosis and referral. One study reported that 55% of patients with ILD receive at least one incorrect diagnosis, while 38% received two incorrect diagnoses before the correct diagnosis is made [4]. Prior thoracic radiotherapy, smoking history or the presence of comorbidities, such as coronary artery disease or gastroesophageal reflux disease, can also further complicate diagnosis.

When symptoms persist or worsen, patients are typically referred to a respiratory specialist. However, around 30% of ILD patients may attend four or more primary care or oncology consultations before referral [4]. Diagnosis often depends on HRCT, and, in some cases, invasive diagnostic procedures, such as SLB, to exclude infection and tumour progression. These investigations can be burdensome for patients already receiving cancer treatment, and contribute to prolonged delays in diagnosis [5].

The Consequences of Delayed Detection

Delays in diagnosing DI-ILD represent a missed opportunity to intervene before permanent lung damage occurs. Persistent inflammation can progress to irreversible fibrosis, which reduces lung elasticity and impairs gas exchange, ultimately leading to permanent respiratory impairment. The early diagnosis of DI-ILD enables the initiation of corticosteroids, which can help reduce inflammation and slow or prevent further lung injury [2,3].

Delays in the diagnosis of DI-ILD are also associated with increased mortality. In one study of patients with fibrotic ILD, 60% of patients in a delayed diagnosis cohort died during follow-up, compared with 50% of patients in a timely diagnosis cohort [6]. Median overall survival was also substantially shorter in the delayed diagnosis group (52.7 months versus 70.7 months) [6]. These findings highlight the importance of timely diagnosis and intervention before the disease progresses to advanced stages.

Delayed diagnosis of DI-ILD also leads to higher healthcare utilisation, including increased emergency department visits, hospital admissions, intensive care unit stays, and longer inpatient length of stay. Patients with prolonged diagnostic delays of more than a year have almost twice the rate of all-cause hospitalisations during the first-year post-diagnosis compared with those diagnosed earlier [7]. These increases place additional pressure on healthcare resources and translate into higher healthcare costs.