Myth: immunotherapy makes the cancer spread faster — that's not what an early scan usually means

This myth usually starts with a scan report. A patient has a follow-up CT or PET-CT a few weeks after starting immunotherapy, and the report notes that the tumour looks bigger, or that a new small spot has appeared. Read in isolation, that sounds exactly like "the treatment made the cancer spread." Nobody handed a report like that is being unreasonable for worrying.

What the report on its own often doesn't explain is that immunotherapy can produce two genuinely different things on an early scan. One is pseudoprogression — a temporary, usually reassuring appearance of growth caused by immune cells arriving at the tumour, not the cancer itself getting bigger. The other is hyperprogression — a real, uncommon phenomenon where growth genuinely does speed up. Both get lumped together, and both get confused with ordinary disease progression that has nothing to do with the treatment at all, which is exactly why the blanket claim "immunotherapy makes cancer spread" persists even though it isn't an accurate description of what usually happens.

Online anecdotes and isolated case reports about hyperprogression add to the confusion, because a rare, genuinely serious event described without context can read as if it's the typical outcome. It isn't — and telling the two phenomena apart is the whole point of this page.

Only your oncology team, looking at your scans and how you're doing clinically together, can say which of these applies to you. This table is for understanding the terms, not for self-diagnosing a scan report.

1. 1

   Check how you're actually doing, not just the scan

   A patient who feels and functions better despite a "bigger" scan — steady weight, steady energy, no new symptoms — is more consistent with pseudoprogression than with real growth. Clinical status is weighed alongside the images, never ignored in favour of them.

2. 2

   Order a confirmatory scan, not an immediate change of plan

   Per iRECIST guidance referenced by NCCN and ASCO, an early increase on imaging is typically rechecked after a defined interval before it is labelled true progression — because pseudoprogression often resolves into a genuine response on the next scan.

3. 3

   Compare the growth rate, not just the size

   One of the more accepted ways researchers describe hyperprogression is by comparing how fast the cancer was growing before treatment against how fast it appears to grow afterward — a size increase alone doesn't establish this, the pace of change does.

4. 4

   Biopsy the growing area, if there's genuine doubt

   In some cases, a sample from the enlarging area can show whether it is mostly immune cells (supporting pseudoprogression) or mostly tumour cells (supporting true growth) — used selectively, not as a routine step for every scan change.

Not automatically, and not on your own. A single early scan showing an increase does not by itself mean immunotherapy has failed or made things worse — it may be pseudoprogression, which typically goes on to respond well to the same treatment without any change of plan. Stopping or switching treatment on the strength of one scan, before a confirmatory image or a clinical review, can mean abandoning a treatment that was actually about to work.

What does matter is speed in the other direction: if you feel genuinely worse in a way that fits the cancer worsening — new or worsening pain, breathlessness, rapid weight loss, or a marked drop in how you're functioning day to day — tell your oncology team promptly rather than waiting for the next scheduled scan. That clinical picture, not the scan number in isolation, is what your team uses to decide whether to continue, repeat imaging sooner, or change the treatment approach.

Either way, the decision belongs to you and your oncology team together, made from your full picture — not from a scan report read in isolation, and not from a story read online about someone else's experience.

• Myth: Immunotherapy Just Boosts Your Immunity — a related misunderstanding of what immunotherapy mechanistically does, and why the name itself causes confusion.
• Myth: Immunotherapy Has No Side Effects — the opposite myth, and the real, monitored side effects that do exist, separate from anything discussed on this page.
• Myth: Immunotherapy Cures All Cancers — why outcomes vary by cancer type and patient, instead of the all-or-nothing picture either myth suggests.
• Immunotherapy at CION Cancer Clinics — the full picture of how CION explains, delivers, and monitors immunotherapy for patients.

This page is for general information and does not replace a consultation. Never change, pause, or stop immunotherapy based on a scan report alone — always discuss it with your treating oncology team first.

Worrying scan results are one of the most common calls we get

A report that says "increased size" or "new lesion" is frightening to read alone, and it's not a sign you've missed something. Ask us directly — our team explains what it actually means, honestly, at no cost.