If a patient is clinically stable (no worsening pain, no decline in KPS), they should continue immunotherapy after an iUPD scan and be re-evaluated 4-8 weeks later to confirm or refute the progression.

Pseudoprogression occurs because the immune system is infiltrating the tumor with T-cells, causing it to swell or look "new" on CT/MRI. True pseudoprogression is relatively rare (~5-10% of cases), but the iRECIST framework ensures that these responders are not deprived of life-saving therapy.

iRECIST MUST NOT be used to justify continuing therapy in a patient who is clinically deteriorating. If the patient has new-onset severe pain, weight loss, or worsening ECOG status, the progression should be considered real regardless of the scan timing.