Successful management of chronic eosinophilic pneumonia triggered by immune checkpoint inhibitor: a case report and literature review

Abstract

Immune checkpoint inhibitors (ICIs) enhance antitumor immunity by blocking inhibitory immune signals, but can lead to immune-related adverse events (irAEs). Therefore, effective management of irAEs is crucial during ICI therapy. We report the case of a 50-year-old man who was referred to our department due to cough and abnormal chest shadows. He was diagnosed with hypopharyngeal cancer, and underwent chemoradiotherapy, resulting in complete remission. However, metastatic tumors were detected, and partial lung resection was performed. After one-year, new metastatic tumors and pleural dissemination were identified. Therefore, treatment with pembrolizumab was initiated. After the treatment with pembrolizumab, chest imaging revealed ground-glass opacity (GGO). Laboratory tests showed elevated eosinophils, and fractional exhaled nitric oxide (FeNO). The findings of bronchoscopy revealed eosinophilic infiltration and intraluminal fibrosis, consistent with chronic eosinophilic pneumonia (EP). Based on these findings, he was diagnosed with pembrolizumab-induced chronic EP. Pembrolizumab was temporarily discontinued, and oral corticosteroids (OCS) were initiated. After the treatment of OCS, his symptoms and GGO were dramatically improved. Subsequently, pembrolizumab was resumed, and the hypopharyngeal cancer remains stable without recurrence of EP. This report presents the first pembrolizumab-induced chronic EP during treatment for hypopharyngeal cancer. The chronic EP was effectively managed with systemic corticosteroid therapy. Furthermore, pembrolizumab was resumed with close monitoring of blood eosinophil counts and FeNO levels, without worsening of EP. The results of the current case suggest that ICI-induced chronic EP is manageable, and in cases where ICI therapy exhibits significant efficacy against cancer, its treatment may be continued with careful monitoring of these parameters.

Keywords: blood eosinophil; corticosteroid; eosinophilic pneumonia; fractional exhaled nitric oxide; immune checkpoint inhibitors; immune-related adverse events; interstitial lung disease.

Figure 1

Clinical course of the patient. Changes in eosinophil counts, and imaging findings on chest CT (A–F, I) and radiography (G, H). (A, B) Pre-treatment with pembrolizumab; (A) metastatic lung nodules in the left upper lobe (S^{1 + 2}, arrow), and (B) no signs of pneumonia. (C, D) Two months after initiating pembrolizumab; (C) improvement of metastatic lung nodules, and (D) onset of GGO in the left lower lobe (arrow). (E) Eight months after initiating pembrolizumab; onset of GGO in the right lower lobe (arrow). (F) Fourteen months after initiating pembrolizumab; onset of GGO in the left lower lobe (arrow). (G) Upon presentation to our clinic; GGO in the left lower lung field (arrow). (H, I) Following OCS therapy; improvement of GGO in the left lower lobe. BAL, bronchoalveolar lavage; CT, computed tomography; GGO, ground-glass opacity; FeNO. fractional exhaled nitric oxide; OCS, oral corticosteroids; TBLB, transbronchial lung biopsy.

Figure 2

Histological findings of transbronchial lung biopsy. (A) Hematoxylin-eosin staining and (B) Elastica-Masson staining of the left lower lobe tissue obtained by transbronchial lung biopsies. (A) Eosinophilic infiltration with degranulation in the blood vessels and around the alveoli (arrows). (B) Deposition of collagen fibers on the luminal side of the alveoli.