Pseudoprogression

What it is

Pseudoprogression is a treatment-related change seen on imaging — typically increased enhancement or apparent growth — that mimics true tumor progression but is actually a reaction to treatment, not the tumor worsening. It often occurs in the first months after chemoradiation (radiation with temozolomide) for glioblastoma.

Understanding Pseudoprogression

After chemoradiation, the treated area can show increased contrast enhancement or apparent enlargement on MRI that looks like the tumor is growing — but in pseudoprogression, this reflects treatment effects (such as inflammation and changes to blood vessels) rather than actual tumor growth, and it tends to stabilize or improve over time without a change in treatment. Distinguishing pseudoprogression from true progression is important but can be challenging, since both can look similar on standard imaging; this is where advanced techniques (such as perfusion MRI, spectroscopy, or PET) and follow-up over time help. Recognizing pseudoprogression prevents prematurely abandoning a working treatment or making decisions based on a false impression of growth. It is more common in tumors with MGMT methylation. Understanding pseudoprogression in gliomas clarifies a treatment effect that can be mistaken for tumor growth.

Why it matters

Understanding pseudoprogression helps patients and families interpret post-treatment scans cautiously — apparent growth can be a treatment effect rather than true progression, so distinguishing the two avoids premature conclusions.