The potential mechanism, recognition and clinical significance of tumor pseudoprogression after immunotherapy

As immunotherapy has gained increasing interest as a new foundation for cancer therapy, some atypical response patterns, such as pseudoprogression and hyperprogression, have garnered the attention of physicians. Pseudoprogression is a phenomenon in which an initial increase in tumor size is observed or new lesions appear, followed by a decrease in tumor burden; this phenomenon can benefit patients receiving immunotherapy but often leads to premature discontinuation of treatment owing to the false judgment of progression. Accurately recognizing pseudoprogression is also a challenge for physicians. Because of the extensive attention on pseudoprogression, significant progress has been made. Some new criteria for immunotherapy, such as irRC, iRECIST and imRECIST, were proposed to accurately evaluate the response to immunotherapy. Many new detection indexes, such as ctDNA and IL-8, have also been used to identify pseudoprogression. In this review, the definition, evaluation criteria, mechanism, monitoring, management and prognosis of pseudoprogression are summarized, and diagnostic and treatment processes for patients with progression but with a suspicion of pseudoprogression are proposed; these processes could be helpful for physicians in clinical practice and enhances the understanding of pseudoprogression.