One of the more confusing situations after glioma treatment is when a follow-up scan looks worse — but the tumor may not actually be growing. This is called pseudoprogression, and understanding it can spare you considerable worry, because it's a known effect of treatment rather than a sign of failure.
What pseudoprogression is Pseudoprogression is an inflammatory reaction to treatment — typically after radiation combined with temozolomide chemotherapy — that shows up on MRI as increased contrast enhancement or swelling, mimicking tumor growth. It isn't the tumor advancing; it's the treatment working and the tissue reacting. It most often appears in the first few months after chemoradiation (especially the first 3 months).
Why it's tricky On a standard MRI, pseudoprogression and true tumor growth can look very similar. Both can show new or increased enhancement. This is why your team interprets scans in context — timing since treatment, your symptoms, and sometimes specialized imaging.
How teams tell them apart. Several approaches help:
- Timing. Changes appearing soon after chemoradiation are more likely to be pseudoprogression.
- Follow-up imaging. Sometimes the clearest answer comes from a repeat scan after a short interval — pseudoprogression tends to stabilize or improve on its own, while true progression continues.
- Advanced imaging. Techniques like MR perfusion, MR spectroscopy, or PET can provide additional clues about whether tissue is active tumor or treatment effect.
- Your clinical picture. Whether you're feeling stable or worsening is an important piece of the puzzle.
A related effect: radiation necrosis Later after radiation (often many months to years), radiation necrosis — damaged tissue at the treatment site — can similarly mimic tumor on scans. Like pseudoprogression, it's a treatment effect, not tumor regrowth, though it sometimes needs its own management.
Why this matters for you If your team mentions possible pseudoprogression, it means they're being appropriately cautious rather than assuming the worst. A scan that looks concerning soon after chemoradiation is not automatically bad news, and your team may recommend a short-interval follow-up rather than immediately changing treatment. This can be an anxious waiting period — it's reasonable to ask your team to explain their thinking and what the plan is.
The key message: after chemoradiation, not every worsening-looking scan means the tumor is growing. Pseudoprogression is a real, recognized phenomenon, and distinguishing it from true progression is a normal part of expert glioma care.