Comparative Analysis of iRECIST and RECIST 1.1 in ICI-Treated Melanoma and NSCLC

Overview

This retrospective study compared iRECIST and RECIST 1.1 criteria for evaluating immune checkpoint inhibitor (ICI) treatment response in melanoma and non-small cell lung cancer (NSCLC) patients. The analysis focused on real-world clinical imaging data to assess the ability of each criterion to capture atypical response patterns such as pseudoprogression.

Background

Immune checkpoint inhibitors targeting CTLA-4, PD-1, and PD-L1 have significantly improved survival outcomes in cancers like melanoma and NSCLC. Traditional response criteria such as RECIST 1.1 may misclassify atypical response patterns, including pseudoprogression, as disease progression, potentially leading to premature treatment discontinuation. To address this, immune-specific criteria like iRECIST were developed to better capture these unique response patterns during ICI therapy. However, evidence comparing iRECIST to RECIST 1.1 in real-world settings remains limited.

Data Highlights

The study included patients treated with ipilimumab, nivolumab, pembrolizumab, or their combinations, who underwent baseline and at least two follow-up contrast-enhanced CT scans. Imaging was performed using various CT systems with slice thicknesses ranging from 2 mm to 5 mm. Treatment response was assessed retrospectively by experienced radiologists according to RECIST 1.1 and iRECIST guidelines.

Key Findings

• iRECIST was specifically designed to account for atypical response patterns such as pseudoprogression, which are not adequately captured by RECIST 1.1.
• RECIST 1.1 may prematurely classify pseudoprogression as progressive disease, risking early discontinuation of effective ICI therapy.
• iRECIST allows for confirmation of progressive disease (iCPD) before treatment cessation, potentially improving patient management.
• The study utilized a real-world cohort of melanoma and NSCLC patients treated with ICIs, enhancing the applicability of findings outside clinical trials.
• Response evaluations were conducted by board-certified radiologists with consensus review to ensure accuracy and consistency.

Clinical Implications

Clinicians should consider using iRECIST criteria when evaluating ICI treatment response to better identify atypical patterns such as pseudoprogression. This approach may prevent premature discontinuation of effective immunotherapy and optimize patient outcomes. Incorporating iRECIST into routine clinical practice could enhance decision-making in managing melanoma and NSCLC patients receiving ICIs.

Conclusion

This study supports the use of iRECIST over RECIST 1.1 for response assessment in melanoma and NSCLC patients undergoing ICI therapy, particularly in real-world clinical settings. iRECIST’s ability to capture atypical response patterns may improve treatment evaluation and patient management.

References

1. RECIST Working Group 2017 -- iRECIST: Guidelines for Response Assessment in Immunotherapy
2. University Hospital Cologne Study 2015-2023 -- Comparative Analysis of iRECIST and RECIST 1.1