[Pseudoprogression after start of immunotherapy].

[CLINICAL/METHODICAL ISSUE] Distinguishing pseudoprogression from true progression represents a considerable challenge in both clinical practice and radiological imaging.

[STANDARD RADIOLOGICAL METHODS] Established radiological methods include computed tomography (CT) and magnetic resonance imaging (MRI), complemented by fluorodeoxyglucose-positron emission tomography (FDG-PET)/CT from nuclear medicine.

[METHODICAL INNOVATIONS] Novel PET/CT tracers, liquid biopsies, and radiomics are considered innovative approaches that may facilitate the detection of pseudoprogression but still need clinical validation.

[PERFORMANCE] CT, MRI, and PET/CT can provide valuable clues for distinguishing pseudoprogression from true progression, but are often inconclusive. Novel imaging approaches are currently under investigation in clinical studies.

[ACHIEVEMENTS] The use of laboratory markers and radiomics has shown promising improvements in several studies, but has not yet been adopted into clinical routine.

[PRACTICAL RECOMMENDATIONS] In clinically stable patients, suspected pseudoprogression early after start of immunotherapy justifies continuation of therapy with close imaging follow-up (early follow-up after 4-8 weeks).