Radiological Monitoring of Modern Immunotherapy: A Novel Challenge for Interdisciplinary Patient Care

Immunotherapy represents an effective therapeutic approach for many malignant diseases that were previously difficult to treat. However, since immunotherapy can lead to atypical therapy response patterns in the form of pseudo-progression or mixed responses and comprise an altered spectrum of adverse reactions, they present a new challenge for oncologic imaging. Detailed knowledge in this area is essential for oncologic clinical radiologists, since the radiological report is a cornerstone of response assessment, and increasingly influences therapy regimens and coverage by health insurances.

This white paper is based on an expert meeting in Frankfurt am Main and subsequent discussions between the authors. Based on the iRECIST criteria, it is intended to provide orientation for a response assessment of oncologic patients undergoing immunotherapy that can be applied in the clinical routine.

Radiological therapy monitoring outside clinical studies is subject to inherent limitations, but should be performed based on iRECIST criteria, according to the opinion of the expert panel. It should be taken into account that immunotherapies can in principle lead to pseudo-progression and autoimmunological side effects. Since radiological follow-up is currently the only method to accurately distinguish real progressive disease from pseudo-progression, clinically stable patients with disease progression under immunotherapy should undergo additional short-term follow-up imaging according to the suspected diagnosis. Biopsy should be used cautiously and predominately in curative settings.

For response assessment of immunotherapy in clinical studies, the new iRECIST criteria were published in 2017. Outside studies, the application of iRECIST criteria in the clinical routine is subject to several limitations. The recommendations implied in these criteria can, however, be used in conjunction with the current literature as a guideline in clinical practice and outside studies.

· Novel immunotherapies can cause atypical response patterns like pseudo-progression. · Compared to real progressive disease, pseudo-progression occurs rather rarely, yet can influence therapy. · Short-term follow-up according to iRECIST can help to distinguish pseudo-progression from real progression. · Hence, radiological follow-up outside clinical studies should be oriented towards iRECIST criteria.

· Lennartz S, Diederich S, Doehn C et al. Radiological Monitoring of Modern Immunotherapy: A Novel Challenge for Interdisciplinary Patient Care. Fortschr Röntgenstr 2020; 192: 235 - 244.