Complex immunotherapy-mediated response patterns depicted on serial 18F-FDG PET imaging of Hodgkin lymphoma patient undergoing pembrolizumab therapy.

Over the past decade, the role of ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) in assessing treatment response for lymphoma patients undergoing immunotherapy has been extensively investigated. The advent of immunotherapy has challenged the utility of the established Lugano criteria, prompting the development of novel immunotherapy-specific response criteria now employed in clinical practice. Following ¹⁸F-FDG PET/CT evaluation after up to eight immunotherapy cycles, patients are typically transitioned to conventional imaging modalities if immunotherapy continuation is warranted. This case report illustrates the application of serial ¹⁸F-FDG PET/CT in monitoring a 67-year-old patient with Hodgkin lymphoma receiving immunotherapy, revealing complex, atypical response patterns unresolved by existing criteria. Notably, two episodes of pseudoprogression occurred at two distinct time points, one during cycle 5 and the other during cycle 22. Furthermore, an immunotherapy-enhanced abscopal effect was seen during radio-immunotherapy, leading to short-term disease remission. Our findings suggest that ¹⁸F-FDG PET/CT provides superior predictive value in delineating heterogeneous response patterns, thereby informing critical decisions regarding immunotherapy cessation or adjunctive therapeutic interventions.