Diagnostic impact of 18F-FDG PET/CT imaging on the detection of immune-related adverse events in patients treated with immunotherapy

Introduction Immunotherapy is an effective treatment method for cancer cells with humoral and cellular immune mechanisms of action but triggers an inflammatory response and disrupts standard protective immune tolerance. Early detection of immune-related adverse events (irAEs) on PET/CT is crucial for patient management and subsequent therapy decisions. In this study, we aimed to evaluate the impact of 18 F-FDG PET/CT on detecting of irAEs in patients receiving immunotherapy. Patients and methods Forty-six patients with advanced RCC ( n : 32), malign melanoma ( n : 9), lung cancer ( n : 4), and laryngeal carcinoma ( n : 1), who underwent 18 F-FDG PET/CT imaging for response assessment after immunotherapy, were enrolled in the study. Newly detected findings associated with irAEs on posttreatment PET/CT images were compared with the pretreatment PET/CT, both qualitatively and semi-quantitatively. Results Twenty-eight (61%) patients developed irAEs as observed on PET/CT. Enteritis/colitis was the most frequent irAE visualized on PET/CT with 13 patients (28.2%), followed by gastritis (17.3%), thyroiditis (13%), and myositis/arthritis (13%). Hepatitis (6.5%), pneumonitis (6.5%), sarcoid-like reaction (4.3%), and hypophysitis (4.3%) were observed to a lesser extent. The median time between the appearance of irAEs on PET/CT and the initiation of immunotherapy was 4.3 months. There were no significant differences in age, sex, and treatment response status of patients with and without irAEs. Conclusion 18 F-FDG PET/CT plays a fundamental role in cancer immunotherapy with the potential to show significant irAEs both in the diagnosis and in follow-up of irAEs. IrAEs were present on PET/CT images of more than half of the patients who received immunotherapy in our study.