[Adverse effects of immunotherapy : Clinical aspects, radiological and nuclear medicine results]

Imaging evaluation of lung cancer treated with PD-1/PD-L1 inhibitors

Immunotherapy (PD-1/PD-L1 inhibitors) has attracted attention for lung cancer treatment and recasted the administration of immunotherapeutics to patients who have advanced/metastatic diseases. Whether in combination or as monotherapy, these medications have become common therapies for certain patients with lung cancer. Moreover, their usage is expected to expand widely in the future. This review aims to discuss the imaging evaluation of lung cancer response to PD-1/PD-L1 therapy with focus on new radiological criteria for immunotherapy response. Abnormal radiological responses (pseudoprogression, dissociative responses, and hyperprogression) and immune-related adverse events are also described.

Pitfalls in the radiological response assessment of immunotherapy

Immunotherapies comprise of a class of cancer therapies that are increasingly used for treatment of several cancer entities. Active immunotherapies encompassing immune checkpoint inhibitors are the most widespread class of immunotherapies, with indications for melanoma, non-small lung cancer, renal cell carcinoma, urothelial carcinoma, head and neck squamous cell carcinoma, and Hodgkin’s lymphoma. Immune checkpoint inhibitors have demonstrated unique response patterns that are not adequately captured by traditional response criteria such das the Response Evaluation Criteria in Solid Tumors (RECIST) and World Health Organization criteria. Consequently, adaptions of these criteria have been released such as the immune-related RECIST and immune RECIST, which account for the specialities of immunotherapies. Immunotherapies can cause a distinct set of adverse events such as pneumonitis, colitis, and hypophysitis. In addition, atypical treatment response patterns termed pseudoprogression have been observed. Thereby, new or enlarging lesions appear after treatment start and mimic tumor progression, which is followed by an eventual decrease in total tumor burden. In this review article we will describe pitfalls in the radiological response assessment of immunotherapies, focusing on pseudoprogression and imaging appearances of common immune-related adverse events.