[Monitoring of immunotherapy : Possibilities and limitations]

Cancer immunotherapies play an increasing role in the treatment of advanced cancer. In a subset of patients, atypical response patterns and unconventional adverse events make diagnostic evaluation challenging for radiologists.

In this article, we provide a review of the possibilities and limitations of imaging methods in monitoring immunotherapies, discuss the phenomena of pseudoprogression and hyperprogression, and introduce iRECIST as an evaluation standard for clinical studies with immunotherapies. In addition, we describe the most notable adverse events and their imaging features.

This article is based on reviews and studies published since 2009. We used PubMed for the literature search and included the following search terms: "immunotherapy", "checkpoint inhibitor", "pseudoprogression", "iRECIST" and "immune related adverse events".

With an incidence of up to 10%, pseudoprogression is a rare phenomenon. Currently, differentiation between pseudoprogression and true progressive disease is only possible by follow-up examinations. iRECIST, published in 2017, introduced immune unconfirmed progressive disease (iUPD) and immune confirmed progressive disease (iCPD) as new categories of therapeutic response. There is still no consensus on the time interval between examinations. Crucial adverse events include hypophysitis and pneumonitis, whereby the latter may present as different patterns of interstitial pneumonia making it difficult to differentiate between drug toxicity, infection, and tumor progression.