Bronchoalveolar lavage fluid analysis in patients with checkpoint inhibitor pneumonitis.

e14683 Background: Checkpoint inhibitor pneumonitis (CIP) is a relatively uncommon but potentially life-threatening immune-related adverse event (irAE). Lung biopsies have not been commonly performed for CIP patients. Bronchoalveolar lavage fluid (BALF) analysis is a useful diagnostic approach for interstitial lung disease. However, BALF features were inconsistent across different studies. Methods: We retrospectively reviewed the medical records of 154 patients with pathologically confirmed malignancies and suffering from CIPs between July 2018 and December 2022. Patients who had bronchoalveolar lavage (BAL) data available were enrolled in our study. Patient clinical, laboratory, radiological and follow-up data were reviewed and analyzed. In our study, patients with grade 1 or grade 2 CIPs were defined as low-grade CIPs, and patients with grade 3, grade 4 or grade 5 CIPs were defined as high-grade CIPs. Results: The BALF differential cell count and lymphocyte subset analysis were performed for 42 CIP patients. There were 32 males (76.2%). The mean age at diagnosis of CIP was 62.0 ± 10.4 (range: 31-78) years. The median time to onset of CIP was 98.5 days after the start of immunotherapy. Most of the patients were diagnosed with lung cancer (36 patients, 85.7%). There were 3 patients with esophageal squamous cell cancer, 1 patient with hepatic cell cancer, 1 patient with gastric signet ring cell cancer and 1 patient with pericardial malignant mesothelioma. There were 18 patients (42.9%) with low-grade CIPs and 24 patients (57.1%) with high-grade CIPs. The mean lymphocyte percentage was 36.7 ± 22.5%. There were 34 (81%) CIP patients with a lymphocytic cellular pattern. The median ratio of CD3 + CD4 + /CD3 + CD8 + lymphocytes was 0.5 (0.3, 1.0). The ratio was less than 1.0 for 31 CIP patients (73.8%). However, there was no significant difference in the BALF features between patients with low-grade CIPs and those with high-grade CIPs. Conclusions: The CD3 + CD8 + lymphocytosis pattern was the main inflammatory profile in the BALF of CIP patients in this cohort. Targeting CD3 + CD8 + lymphocytes might be a treatment option for CIPs.