Pseudoprogression

What pseudoprogression is

Cancer treatments damage tumor cells and blood vessels and trigger inflammation. On MRI or CT, that inflammation can look exactly like tumor: a mass that enlarges, more contrast "enhancement" (areas that light up after dye) and more swelling around it. With time, the changes stabilize or shrink without any change in treatment. That is pseudoprogression.

The opposite, true progression, means the cancer is genuinely growing. Because the two look similar on standard scans, doctors use timing, symptoms and specialized imaging to tell them apart.

Pseudoprogression in brain tumors

Glioblastoma and gliomas

Standard treatment for glioblastoma is surgery, then radiotherapy with temozolomide chemotherapy. Roughly 20% to 30% of patients have scans in the first 3 months after treatment that look worse. Many of these are pseudoprogression. It is more common in tumors with MGMT promoter methylation, a tumor feature that predicts a better response to temozolomide, and pseudoprogression itself is often linked with a better outlook.

The RANO criteria, which neuro-oncologists use to assess response, advise caution in calling progression within 12 weeks after radiotherapy unless there is new enhancement outside the radiation field or a biopsy confirms tumor. The updated RANO 2.0 criteria recommend confirming suspected early progression with a follow-up scan.

Pseudoprogression vs radiation necrosis

See radiation necrosis for more on the later effect.

Symptoms

Many people have no new symptoms, and pseudoprogression is found on a routine scan. When swelling is significant, people may have:

• headaches, nausea or vomiting
• seizures
• worsening weakness, speech or vision problems
• tiredness and confusion

These symptoms are not specific: true progression and brain swelling from other causes can produce the same picture.

Pseudoprogression with immunotherapy

Checkpoint inhibitor drugs, such as pembrolizumab, nivolumab and ipilimumab, help immune cells attack cancer. As immune cells flood into a tumor, it can swell or new small spots can appear before the cancer shrinks. Some tumors also appear to grow because the immune response takes several weeks to build.

• It is most often reported in melanoma, where it occurs in a minority of patients (under about 10%), and less often in lung cancer, kidney cancer and other tumors.
• Most true growth on immunotherapy is real progression, so pseudoprogression should not be assumed.
• Response criteria for immunotherapy (iRECIST) label early growth as "unconfirmed progression" and recommend a repeat scan, usually 4 to 8 weeks later, before deciding.
• Treatment is usually continued only if the person is clinically stable or improving.

A separate pattern, hyperprogression, describes rapid real tumor growth after starting immunotherapy. It is the reverse of pseudoprogression and needs a quick change in treatment.

How doctors tell pseudoprogression from true progression

1. Timing: how long after radiotherapy or immunotherapy the change appeared.
2. Clinical picture: whether you are stable, improving or getting worse.
3. Short-interval repeat scans: often 4 to 8 weeks later. Pseudoprogression stabilizes or shrinks. True progression keeps growing.
4. Advanced MRI: perfusion MRI shows blood volume in the lesion, which tends to be low in treatment effect and high in active tumor. MR spectroscopy measures chemical markers of tumor activity, and diffusion imaging adds clues.
5. Amino acid PET: tracers such as FET, FDOPA or fluciclovine highlight active tumor cells.
6. Biopsy or surgery: the most definitive, used when imaging remains unclear or surgery is needed to relieve pressure.

No single test is perfect. A tumor board with radiologists and oncologists usually reviews uncertain cases.

Treatment

• Continue current treatment if pseudoprogression is likely and you are stable.
• Corticosteroids such as dexamethasone reduce brain swelling and symptoms, using the lowest effective dose for the shortest time.
• Bevacizumab may help significant symptomatic swelling or radiation necrosis.
• Seizure medicines if seizures occur.
• Surgery to remove a mass causing pressure, which also provides a tissue diagnosis.

Frequently asked questions

What is pseudoprogression in cancer?

It is an apparent increase in tumor size, or new areas of enhancement, seen on a scan after treatment, caused by inflammation, swelling or immune cells rather than cancer growth. It settles or improves over time without changing treatment. It is most common after brain tumor chemoradiation and immunotherapy.

How common is pseudoprogression in glioblastoma?

Studies suggest about 20% to 30% of people with glioblastoma have changes on early post-treatment scans that turn out to be pseudoprogression. It typically appears within 3 months of finishing radiotherapy with temozolomide and is more common in tumors with MGMT promoter methylation.

How do you tell pseudoprogression from real progression?

Doctors consider timing after treatment, symptoms and repeat scans. Perfusion MRI, MR spectroscopy and amino acid PET give further clues, and a biopsy can settle doubt. Pseudoprogression stabilizes or shrinks on follow-up scans, while true progression continues to grow.

Is pseudoprogression a good sign?

Often it is. In glioblastoma, pseudoprogression is associated with a good response to treatment and longer survival. On immunotherapy, it reflects an active immune response. It still needs careful monitoring, because it can be hard to distinguish from real progression at first.

How long does pseudoprogression last?

In brain tumors, it usually appears within the first 3 months after radiotherapy and settles over the following weeks to months. With immunotherapy, apparent growth is generally seen in the first few months and is followed by stabilization or shrinkage on later scans.