Paul A. Bunn Jr, MD
Pseudoprogression, which has been observed in less than 10% of patients with lung cancer, occurs when an early scan shows tumor growth that may be due to a delayed benefit of the immunotherapy treatment or inflammation of the tumor as T cells become active. When a patient does respond to immunotherapy, the benefits can be long lasting.
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How do you define pseudoprogression?
Pseudoprogression is when it appears that the tumor is getting larger, but the patient is responding. If you have a tumor and the lymphocytes come in and kill the cancer, because of all the lymphocytes, the tumor might seem bigger in the scan, whereas the tumor may actually be smaller. That seems to happen more often in melanoma, but it clearly can happen in lung cancer.
An advantage of neoadjuvant care is you have the scan, but you also have the surgical specimen. If there are a bunch of lymphocytes in the surgical specimen and the tumor is gone or much smaller, you can actually see that. From preliminary data on less than 50 patients and 2 trials, there is no question that you can have major pathologic responses in the absence of a CT response because of all the infiltration of lymphocytes.
Why is pseudoprogression a concern when you’re treating patients with immunotherapy?
For those people who benefit from immunotherapy, the responses frequently last a very long time. They occur in a minority of patients, so if they do occur, you don’t want to deprive the patient of the ability to have a long response.
How often does pseudoprogression occur in lung cancer?
True pseudoprogression in lung cancer is not that common. It is true that patients with Response Evaluation Criteria in Solid Tumors [RECIST] stable disease may have a true pathologic response. We’ve seen that in the early neoadjuvant trials, but with stable disease and immunotherapy, if the patient is doing well, you could continue the treatment. The big issue is if the tumor is 20% larger or more, which is RECIST progression, if that patient is having pseudoprogression because of the lymphocytes, you don’t want to stop the treatment. Having it get 20% bigger and have a response is not that common, but it can occur. So, what do you do? When that happens, it occurs early. So if the patient is doing well, their symptoms go away, and they seem to be benefiting, you could continue for 1 or 2 more [cycles of] treatment and repeat the CT scan. If the patient is deteriorating and the scan is getting worse, you obviously stop the treatment.
What should community oncologists know about the difference between pseudoprogression and real progression?
They should know that if the patient’s tumor got bigger and the patient has not gotten better, they should stop the treatment. But if early on the tumor got 25% bigger and the patient’s symptoms went away, they can consider continuing.
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