A special case of “pseudoprogression” can occur with PD-1/PD-L1 inhibitors.
“Pseudoprogression” is characterized by a transient increase in tumor size or diameter during PD-1/PD-L1 inhibitor therapy, or by the appearance of new lesions that later shrink. As the number of patients using PD-1/PD-L1 inhibitors increases and the range of indications expands, approximately 7% to 10% of the population receiving immunotherapy experiences a “pseudoprogression” in which tumor lesions increase in size and then decrease in size.
Incidental tumor enlargement is caused by excess lymphocytes infiltrating the tumor tissue, and new lesions appear because the lymphocytes have not had time to infiltrate and attack the tumor tissue, not because the treatment is ineffective.
Co-reviewed by: Guangdong Provincial People’s Hospital Guangdong Provincial Lung Cancer Institute Dr. Wang Zhen, Deputy Chief Physician Sun Hao