When Should You Have a PET-CT — After Immunotherapy?

There is no single answer — the right timing depends on your cancer type, the specific drug, and the protocol your oncologist is following. What is consistent across ASCO and ESMO guidance is that the first assessment scan tends to come later with immunotherapy than with chemotherapy, to allow enough time for a genuine response to become visible and to avoid the misleading picture an early scan can produce. Ask your oncologist when the first scan is planned and why they have chosen that point.

Not necessarily, and this is one of the most important differences between immunotherapy and other treatments. ASCO and ESMO guidance is that apparent progression on immunotherapy should be confirmed on a second scan before treatment decisions are made — unless you are clearly getting worse clinically. If you feel stable or better, your oncologist will very likely book a confirmatory scan rather than stopping treatment immediately. One scan showing growth is a question, not a final answer.

Pseudoprogression is when a scan looks worse because immune cells are flooding the tumour — the apparent growth is inflammation, not cancer. Hyperprogression is the opposite: a real, rapid acceleration of tumour growth that a minority of patients experience on immunotherapy. Both can look similar on a single scan. The difference is established by the confirmatory scan and by your clinical condition — whether you feel better, the same, or clearly worse. Your oncologist monitors both your imaging and how you are doing to distinguish them.

You can always raise your concerns, and your oncologist should explain their reasoning. In most cases, scanning earlier than planned does not give you better information — it gives you information that is harder to interpret, because pseudoprogression makes early results ambiguous. If you are feeling clearly worse, have new symptoms, or are losing weight, raise that with your team immediately. Clinical deterioration changes the calculus and needs to be reported regardless of when the next scan is scheduled.

iRECIST is a set of criteria developed by ESMO to assess how cancer responds to immunotherapy on scans. The key difference from standard RECIST — designed for chemotherapy — is that iRECIST requires apparent progression to be confirmed at a second scan before it is treated as real. This matters to you because it is the framework that stops a working treatment from being abandoned too early based on a single scan. It is why your oncologist will not change course on the strength of one result alone.

Yes. PET-CT scans are coordinated with partner imaging centres as part of your treatment plan at CION. Your oncologist determines the timing based on your specific cancer type and protocol. Immunotherapy is administered as day care at CION centres, and scan scheduling is built into the follow-up plan. If you are unsure when your next scan is due or what it will assess, ask your oncology team at your next visit.