[Pseudoprogression after start of immunotherapy]

Distinguishing pseudoprogression from true progression represents a considerable challenge in both clinical practice and radiological imaging.

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

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

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.

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

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).