SUV values rising on your PET scan after immunotherapy — what that number can and can't tell you

SUV can rise after immunotherapy starts because the PET tracer collects wherever cells are using more glucose — and immune cells activated by checkpoint inhibitors are metabolically active enough to light up on a scan too. A higher number at or near a tumour, or in a nearby lymph node, does not automatically mean the cancer itself has grown.

SUV, or Standardized Uptake Value, is the number radiologists use to describe how much of the radioactive tracer — usually FDG, a labelled form of glucose — a tissue absorbs on a PET-CT. Cancer cells often show high uptake because they use glucose faster than most normal tissue, which is why a rising SUV is usually read as a sign of more active disease. Immunotherapy complicates that reading because the immune cells it activates — T-cells gathering at a tumour, or a reactive lymph node — are themselves glucose-hungry and can raise the number without any real increase in cancer.

A rise can also come from causes that have nothing to do with cancer or immunotherapy directly — recent infection, inflammation elsewhere in the body, or normal physiological uptake in muscle, brown fat or bowel. Checkpoint inhibitors are also associated with a recognised sarcoid-like reaction, where new FDG-avid lymph nodes or lung nodules appear that reflect immune granulomas rather than cancer spread.

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

Categories describe general patterns discussed in oncology literature on immunotherapy imaging, indicative as of August 2026. This is patient education, not an interpretation of any individual scan — only your oncologist can assign which pattern applies to your report.

1. 1

   Your team checks the timing

   A rise seen in the first 8-12 weeks of immunotherapy is reviewed differently from one appearing much later, since the flare window is earliest in treatment.

2. 2

   The whole scan is read, not just the number

   Radiologists look at lesion size, the location and pattern of new uptake, and compare it with your previous scan rather than one SUV in isolation.

3. 3

   Your symptoms and how you're doing are weighed alongside it

   Feeling stable or improving is a genuine clinical signal that's considered together with the imaging, not overridden by it.

4. 4

   A confirmatory scan usually follows

   Repeating the PET a few weeks later is what actually settles whether the uptake keeps rising (true progression) or falls back (a flare).

Checkpoint inhibitors don't shrink a tumour directly — they release a brake on your own T-cells, which then travel to the tumour and to nearby lymph nodes to do that work. Because activated immune cells burn glucose quickly, a site with a lot of immune-cell traffic can show high FDG uptake on a scan even while the tumour underneath is responding well.

How often this happens, and in which cancer types it's most documented, is still being defined — checkpoint-inhibitor imaging literature describes it most consistently in melanoma and lymphoma, with less data in other tumour types. If your cancer type isn't one where this pattern is well studied, raise that directly with your oncologist rather than assuming either way.

• New or worsening symptoms — pain, breathlessness or new lumps that are genuinely getting worse, not just a number changing.
• Lesion size increasing alongside SUV — uptake rising together with the tumour actually getting bigger on CT measurements.
• Growth at multiple, unrelated sites — several new or enlarging areas at once reads differently from a single new spot.
• Continued rise on the repeat scan — this, more than anything else, is what confirms true progression.
• Falling performance status — a real decline in your ability to manage daily activities, rather than how you feel on a given day.

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

• New Lymph Nodes Lighting Up on Your Scan — a closely related pattern behind the reactive-node row in the table above.
• Tumour Markers on Immunotherapy: Why They Are Less Useful — why blood markers alone often can't settle what a rising SUV can't either.
• How Often Will You Be Scanned on Immunotherapy? — when the confirmatory scan mentioned above is typically scheduled.
• Immunotherapy at CION Cancer Clinics — the full picture of how CION supports patients through the immunotherapy decision and journey.

This page explains general terminology behind a rising SUV on a PET-CT 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 a scan number that didn't make sense

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