Immune check‐point inhibitor‐related pneumonitis: acute lung injury with rapid progression and organising pneumonia with less severe clinical disease

Aims To improve understanding of the pathology of immune check‐point inhibitor (ICI)‐related pneumonitis, clinical, radiographic and histopathological features and outcomes were investigated in a cohort of patients who were treatment‐naive before receiving ICI inhibition, who underwent lung biopsy, and in whom other potential causes of lung injury were excluded. Methods Patients were retrospectively identified via searches of institutional pathology and clinical records. Patients treated with other modalities for cancer and patients with lung infections or other aetiologies that could cause pneumonitis were excluded. Clinical records were reviewed by pulmonologists. Imaging studies at presentation and follow‐up were reviewed by a thoracic radiologist. Pathology was reviewed by thoracic pathologists. Results Six patients with ICI‐related pneumonitis were identified. Two patients presented with respiratory failure requiring mechanical ventilation, diffuse ground glass opacities (GGOs) on chest computed tomography (CT) and acute lung injury (ALI) pattern on transbronchial lung biopsies and had fatal outcomes, despite treatment. The remaining four patients presented with less severe symptoms, predominantly consolidations and patchy ground glass and part solid opacities on chest CT, organising pneumonia (OP) or chronic interstitial inflammation histologically, and showed favourable responses to treatment and remission within months. Conclusions This study highlights two radiological–pathological patterns of ICI‐related pneumonitis with different behaviour: (1) severe respiratory symptoms and diffuse GGOs on imaging correlating with ALI pattern histologically and poor prognosis; and (2) mild respiratory symptoms and consolidations or patchy subsolid opacities on imaging correlating histologically with OP or chronic interstitial inflammation and good outcomes.