Comparison of Pneumonitis Rates and Severity in Patients With Lung Cancer Treated by Immunotherapy, Radiotherapy, and Immunoradiotherapy.

Introduction Radiation pneumonitis (RP) is a common dose-limiting toxicity of radiotherapy to the chest in lung cancer patients. Similarly, the revolutionary use of immune checkpoint inhibitors (ICIs) to treat lung cancer can be complicated by immune-related adverse events (irAEs), particularly checkpoint inhibitor pneumonitis (CIP). Our study aimed to assess the effect of immunotherapy, with and without radiotherapy, on pneumonitis and other outcomes. Methods We performed a retrospective chart review of 680 lung cancer patients treated with either radiotherapy, immunotherapy, or both at St. Luke's University Health Network to determine the incidence rates of pneumonitis. Then, a more extensive review of 346 patients was completed, 181 of whom had pneumonitis, to investigate risk factors and outcomes. Results All-grade pneumonitis incidence was 26.6% while more severe pneumonitis (grade 3 or higher) was 13%. Receiving programmed cell death-1 (PD-1) or ligand-1 (PD-L1) inhibitors, having squamous cell carcinoma (SCC), and having poorer performance status were independently and significantly associated with increased risk of pneumonitis, with AOR (adjusted odds ratios) of 8.32, 4.10, 2.91, and 1.71, respectively. Among those who had pneumonitis, more severe cases (grade 3 or higher) were related to immunotherapy, either alone (58.32%) or with radiation (55.7%), compared to radiation therapy alone (36.2%). Poorer performance status (defined as a higher Eastern Cooperative Oncology Group (ECOG) score) was the only covariate we found to be significantly and independently associated with reduced odds of 18-months survival. More of the patients treated with both lung radiation and immunotherapy had progressive disease (53.8%) compared to those treated with only radiation (30.4%) or immunotherapy (36.7). Progressive disease occurred more in patients with pneumonitis grade 3 or higher (48.3%) than those with no or low-grade pneumonitis (27.2%). Conclusion Receiving PD-L1 and PD-1 inhibitors, either with or without radiotherapy, was associated with a higher risk of more severe pneumonitis (PD-L1 > PD-1) than radiotherapy alone. Given its high incidence and complications, more about therapy-induced pneumonitis is yet to be studied. Learning more about pneumonitis' risk factors and complications is of great clinical importance, as it may result in better treatment planning and improved outcomes. Future studies are needed to investigate the suggested association between symptomatic pneumonitis and poorer response to treatment and whether SCC increases the risk of higher-grade pneumonitis.