Atypical patterns of responses in the era of immune checkpoint inhibitors in head and neck cancer.

The discovery and implementation into everyday clinical practice of immune checkpoint inhibitors (ICIs) has marked a therapeutic renaissance in the treatment of advanced solid tumors. In head and neck cancer, nivolumab and pembrolizumab have both been approved for recurrent/metastatic disease based on robust clinical activity observed in landmark phase III clinical trials. Despite tremendous improvements in overall survival, patterns of response and progression to ICIs may be distinct from those traditionally described with classical chemotherapy or molecularly targeted therapies. In this context, pseudoprogression is observed in patients treated with ICIs that show response after a transient increase in tumor burden and hyperprogression is described as rapid radiological or clinical progression after immunotherapy. Most importantly, the assessment of radiological response in patients receiving ICIs needs to be differentiated. In this review, we aim to describe radiologic criteria for immune response evaluation and illustrate the newly reported concepts of atypical patterns of response to ICIs.