Real-world incidence and risk factors of pneumonitis in chemoradiation plus immune checkpoint inhibitors compared with chemoradiation alone in lung cancer: a retrospective cohort study

Background: Immune checkpoint inhibitors (ICIs) have shown high efficacy in lung cancer. Adding ICIs to chemoradiation might increase the treatment efficacy, while the application of ICIs or chemoradiation alone can induce treatment-related pneumonitis, so whether combination therapy would increase the risk of pneumonitis needs careful evaluation. This study aimed to retrospectively analyze the incidence of pneumonitis in patients who underwent chemoradiation combined with ICIs compared with chemoradiation alone and explore the risk factors of pneumonitis in combination therapy. Methods: This was a retrospective cohort study. Patients who received conventional thoracic radiation with a minimum total dose of 50 Gy for lung cancer between January 2020 and December 2021 at West China Hospital were retrospectively reviewed and followed up for at least 6 months after radiation. Patients were divided into two groups according to whether chemoradiation was administered with or without ICIs. Pneumonitis was evaluated by chest computed tomography (CT) at least every 2 months in outpatient department. The clinical characteristics, including sex, age, smoking history, pathological diagnosis, baseline pulmonary disease [including chronic obstructive pulmonary disease (COPD) and interstitial lung disease (ILD)], treatment strategy, location of primary tumor and radiological dosimetric parameters were recorded. Chi-squared tests or Fisher's exact tests were performed to analyze the difference between the combination group and control group for categorical variables and Mann-Whitney U test for continuous variables. Univariate and multivariate analyses were performed by logistic regression. Results: A total of 152 patients who received chemoradiation were enrolled. The median age was 59 years. A total of 115 (75.7%) patients were non-small cell lung cancer (NSCLC), 22 (14.5%) were small cell lung cancer (SCLC), and 15 (9.9%) were other pathological types. Among them, 58 received chemoradiation combined with ICIs and 94 received chemoradiation alone. The rate of grade >= 2 pneumonitis was significantly higher in the combination therapy group (39.7% vs. 22.3%, P=0.028) and was associated with the use of ICIs [odds ratio (OR): 2.641, 95% confidence interval (CI): 1.244-5.608, P=0.011] and percent volume of the lung receiving >= 30 Gy (V30) (OR: 1.728, 95% CI: 1.214-2.460, P=0.002). The history of chronic lung disease was the independent risk factor (OR: 6.359, 95% CI: 1.953-20.705, P=0.002) of grade >= 3 pneumonitis. In the combination group, univariate and multivariate analyses revealed that V5, V20, V30, and mean lung dose (MLD) were not associated with pneumonitis, whereas the history of chronic lung disease was an independent risk factor of grade >= 3 pneumonitis (OR: 8.351, 95% CI: 1.469-47.484, P=0.017). Conclusions: The incidence of pneumonitis of ICIs combined with chemoradiation was higher than chemoradiation alone, but manageable. The combination therapy should be applied with caution especially in patients with history of chronic lung disease.