Feeling better but the scan looks worse — which one should you trust?

Yes — feeling noticeably better while a scan reports growth, or a new spot, is a documented pattern with this class of drug, not a rare glitch. Immune checkpoint inhibitors work by activating your own immune cells, and those cells then gather in and around a tumour to do their work. That gathering of immune cells — sometimes with mild swelling or inflammation — can itself look like the tumour growing on an early scan, before it reflects any real increase in cancer.

NCCN and ASCO both describe this pattern, generally called pseudoprogression, as a known and expected possibility with checkpoint inhibitors. It doesn't happen to everyone, and it is more extensively documented in melanoma trials than in most other cancer types — but when it does happen, the disconnect between "I feel better" and "the report says worse" is exactly what makes this moment so unsettling.

Response-assessment PET-CT and other imaging for CION patients is coordinated through partner imaging centres. This page explains the general reporting terminology behind this pattern; it does not interpret your specific scan.

Categories shown follow the iRECIST framework developed by the RECIST working group and referenced in NCCN/ASCO guidance for trials of immune checkpoint inhibitors, indicative as of August 2026. This table is general education, not an interpretation of any individual scan — your oncologist assigns the category that applies to your report.

1. 1

   Your team checks the timing

   Growth seen in the first 12 weeks of immunotherapy is reviewed differently from growth appearing much later, since the pseudoprogression window is earliest in treatment.

2. 2

   Your clinical picture is reviewed alongside the scan

   Symptoms, performance status and how you're functioning day to day are weighed together with the imaging finding, not set aside because of it.

3. 3

   If you're stable, treatment usually continues

   Without rapid clinical decline, most protocols keep the current plan running rather than switching off a single, unconfirmed scan result.

4. 4

   A confirmatory scan follows 4-8 weeks later

   This repeat scan is what actually settles the question — further growth points to true progression, while shrinkage or stability points to pseudoprogression.

Immune checkpoint inhibitors don't attack the tumour directly — they release a brake on your own T-cells, which then travel to the tumour site to do the work. When a large number of immune cells arrive together, the area can swell and become inflamed, sometimes enough to measure larger on a scan even while the actual cancer is starting to break down underneath that immune activity.

This is genuinely more documented in some cancers than others — melanoma trials describe it most often, while data in several other tumour types is thinner. Say plainly: if your cancer type isn't one where this pattern is well studied, that uncertainty is worth raising directly with your oncologist rather than assuming either way.

• New or worsening symptoms — pain, breathlessness or swelling that is genuinely getting worse, not just a scan number changing.
• Falling performance status — a real decline in your ability to manage daily activities, rather than how you happen to feel on a given day.
• Growth at multiple sites at once — several new or enlarging areas together is read differently from a single new spot.
• Continued growth on the repeat scan — this, more than anything else, is what confirms true progression under iRECIST.
• Worsening blood markers alongside the scan — tumour markers or organ function tests trending the wrong way add weight to a progression call, though they are never read alone.

If you notice rapid symptom worsening, contact your oncology team promptly rather than waiting for a scheduled follow-up — this page explains general patterns, it does not triage individual symptoms.

• iRECIST: How Response Is Measured Differently for Immunotherapy — the full response framework behind the category table above.
• Partial Response and Complete Response: What the Words Mean — what your report means once a response, not just stability, is confirmed.
• Hyperprogression: When Cancer Accelerates on Treatment — the rarer, opposite pattern this page's checks also help rule out.
• Immunotherapy at CION Cancer Clinics — the full picture of how CION supports patients through the immunotherapy decision and journey.

This page explains general reasons symptoms and scans can disagree during immunotherapy, for education only, and does not interpret any individual patient's report. Response-assessment PET-CT is coordinated at partner imaging centres. Bring your report to a consultation for a doctor's assessment of what it means for you.

Thousands of families have sat with confusing scan reports

A report that seems to contradict how you feel is one of the hardest moments in treatment. Our oncologists take the time to explain what it may mean and what typically happens next.