Immunotherapy has had increasing use in Medical Oncology for a diverse range of primary malignancies. There are various types of immunotherapy which are grouped based on mechanism of action. In recent decades, the immune checkpoint inhibitors (ICI) immunotherapies have been at the forefront of Medical Oncology, sparked by very encouraging results. Some patients with metastatic cancer who were previously deemed palliative were seeing durable response rates and significant increased survival with ICIs. The mechanism of action of ICIs vary wildly compared to the conventional, cytotoxic chemotherapy, upon which traditional radiology response criteria were based and validated upon. Novel responses such as pseudo progression, disease response in the context of new metastases and prolonged stable disease were observed and correlated with improved patient survival with ICI. New radiology response criteria were proposed to better capture disease response to ICI; however, the criteria have been applied heterogeneously and there is continued work in this sector. In addition to the novel responses, ICIs have been linked to numerous, diverse immune-related adverse events (irAE) affecting multiple systems. A large majority of these are mild, but some irAEs are life threatening. Only some of the irAEs have radiological manifestations. It is important that the reporting radiologist recognises potential irAE so clinical teams can be alerted, ICI treatment paused or cessated and steroid treatment initiated. This review will discuss the evolution of the radiology response criteria in ICI and the varied radiological appearances of irAE.
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