A potential mechanism of the onset of immune-related pneumonitis triggered by anti-PD-1 treatment in a patient with advanced adenocarcinoma lung cancer: case report

BACKGROUND: In recent years, the application of immunotherapy combined with chemotherapy in the first-line lung cancer has showed significant benefit in improving long-term survival. Immunotherapy also has risks of immune-related pneumonitis (IRP) after long-term treatment. Despite the treatment strategy of the IRP has been very clear. However, the mechanism is unclear. CASE PRESENTATION: A 73-year-old male patient was diagnosed with left lung adenocarcinoma IVa, EGFR, ALK, ROS1 negative. The patient received anti-PD1 antibody combined with pemetrexed and cisplatin. After 5 cycles of treatment, partial response was obtained. Subsequently, the patient continued the treatment of anti-PD1 antibody combined with pemetrexed. Before the 7th cycle, the CT found a new lesion in the basal segment of the right lower lobe. It was diagnosed with IRP and pneumocystis jirovecii. The patient did not give trimethoprim–sulphamethoxazole (TMP–SMX) and corticosteroids, symptoms and radiological lesions had improved. We describe the report of immune-related pneumonitis trigged by anti PD-1 and monitored the dynamic changes of CD(4+), CD(8+) T lymphocytes, MDSC and Treg cells in the bilateral bronchoalveolar alveolar lavage fluid. From the point of view of immune cells, the mechanism of immune reconstitution inflammatory syndrome is confirmed. Based on the current case report and literature, this study proposes a potential mechanism of the onset. CONCLUSION: Immune reconstitution inflammatory syndrome may be potential mechanism of IRP. This study may improve our understanding of the pathogenesis underlying IRP. We believe the detection and dynamic monitoring CD4(+), CD8(+) T lymphocytes, MDSC and Treg cells can provide more accurate procedures.