Checkpoint inhibitors can make tumours look bigger before they shrink (pseudoprogression) — iRECIST requires confirmation of progression — and cause immune-related adverse events (pneumonitis, colitis, hypophysitis, thyroiditis, sarcoid-like nodes) that the report must name.
Orient first
- iRECIST: first progression is "unconfirmed" (iUPD) and needs confirmation on the next scan at 4–8 weeks (iCPD) — verify.
- Hyperprogression is rapid growth early in treatment.
- Sarcoid-like mediastinal nodes on immunotherapy are often an adverse event, not progression.
Acquire the study
- Portal venous phase CT chest-abdomen-pelvis, same technique each time.
The manoeuvre
- Target lesions measured in mm per RECIST 1.1 / iRECIST (use the calculator).
- New lesions: iUPD — recommend confirmation on the next scan.
- Lung window: pneumonitis pattern (organising pneumonia, NSIP).
- Bowel wall thickening (colitis); pancreas and liver changes.
- Symmetric hilar and mediastinal nodes (sarcoid-like).
What confirms it
- Confirmed progression on a subsequent scan (iCPD), or response by criteria.
What licenses you to exclude it
- One scan with new lesions cannot establish progression under iRECIST.
The classic misread
- Calling pseudoprogression progression after one scan.