Utility of iRECIST for evaluating treatment efficacy in patients receiving immune checkpoint inhibitors

OBJECTIVE: Immune checkpoint inhibitors (ICIs) have shown promising results in treating gynecologic malignancies. However, they may induce a unique response pattern known as pseudoprogression (PP), which can be misclassified as true progression, leading to premature discontinuation of effective therapy. To address this challenge, immune-related Response Evaluation Criteria in Solid Tumors (iRECIST) were developed. This study aimed to assess the utility of iRECIST and to characterize cases that may benefit from its application. METHODS: We retrospectively reviewed 64 patients with gynecologic cancers treated with ICIs at our institution. Tumor responses were evaluated using both RECIST version 1.1 and iRECIST. Cases initially showing tumor enlargement but continuing the same regimen were further analyzed if subsequent imaging demonstrated tumor shrinkage. RESULTS: The cohort's ages ranged from 38 to 83 years (median=62). The cohort included 34 patients with endometrial cancer and 25 with cervical cancer. ICIs used included pembrolizumab (n=59) and cemiplimab (n=5). Among the 64 cases, 3 exhibited tumor changes consistent with PP. In one case, progressive disease was initially observed, but later imaging revealed tumor regression, ultimately achieving complete response. These cases highlight the utility of iRECIST in distinguishing PP from true progression. However, no consistent histologic type or tumor location was associated with PP. Notably, cases showing tumor enlargement after the first CT scan did not subsequently show shrinkage. CONCLUSION: Although PP incidence remains low, these findings suggest that continuing treatment beyond initial progression may be beneficial in select cases. However, since this study is retrospective, further validation is necessary.