Patterns of response in metastatic NSCLC during PD-1 or PD-L1 inhibitor therapy: Comparison of the RECIST 1.1 and iRECIST criteria

Background Immunotherapy plays an important role in advanced non-small cell lung cancer (NSCLC). However, radiological evaluation is challenging due to the potential inflammatory effects of immunotherapy, which can lead to atypical response patterns. Identifying these atypical responses is critical to making treatment decisions and prognostication. Methods We performed a retrospective analysis of consecutive advanced NSCLC patients treated with immunotherapy (alone or in combination). We collected patients' clinical and pathological data, analyzed the proportion of patients who continued immunotherapy beyond progressive disease (PD) per RECIST 1.1, and compared the differences in response patterns between the RECIST 1.1 and iRECIST criteria. Results A total of 43 patients treated at the Peking Union Medical College, China from January 2018 to April 2019 were included. Continued immunotherapy beyond PD per RECIST 1.1 was observed in 10 (33.3%, 10/30) patients, of which there were discordant assessments (30%, 3/10) between the RECIST 1.1 and iRECIST, which were evaluated as PD by RECIST 1.1 and immune unconfirmed PD by iRECIST. Among seven patients with immune confirmed PD, one (1/30, 3.3%) had pseudoprogression. Patients who continued immunotherapy beyond PD (n = 10) experienced significantly prolonged overall survival (not reached vs. 8.1 months: hazard ratio, 2.8; 95% confidence interval: 2.7-13.6, P = 0.03) compared with patients who did not continue immunotherapy beyond PD (n = 20). Conclusions RECIST 1.1 evaluation underestimated the benefit of immunotherapy. Further research is required to optimize iRECIST and establish some criteria for selecting patients who will benefit from continued immunotherapy beyond PD per RECIST 1.1.