Atypical response patterns in Chinese patients with cancer with immune checkpoint blockade

e14631 Background: As specific patterns of progression, atypical responses, including pseudoprogression (PsPD) and dissociated response (DR), have been recently described. The purpose of the present study was to evaluate the frequency and prognosis of PsPD and DR in Chinese cancer patients treated with immune checkpoint inhibitors. Methods: We retrospectively reviewed patients with advanced cancer who received PD-1/PD-L1 inhibitor alone or combination therapy in a single center between December 2019 and January 2022. We evaluated all measurable lesions in each organ to identify PsPD and DR independently of RECIST 1.1. PsPD was defined as RECIST-defined progression followed by stabilization or decrease at the next imaging, and DR as concomitant decrease in some lesions and increase in others or emerging new lesions at a same timepoint. Progression‐free survival (PFS) and overall survival (OS) was compared between patients with atypical responses and those with true response (CR/PR) or nonresponse (SD/PD) using Cox proportional hazards models. Results: The present study included 178 patients aged 18-81 years (median: 63 years). The overall response rate was 18.5%. PsPD and DR were observed in 12 (6.7%) and 7 (3.9%) patients, respectively, and were not associated with any patient’s baseline characteristics. Median PFS (10.9 vs. 5.3 months; p=0.041) and OS (24.1 vs. 13.2 months; p=0.010) was significantly longer in patients with atypical response versus nonresponse, but shorter versus true responses (PFS: 10.9 vs. 35.4 months; p=0.009; OS: 24.1 vs. NR months; p=0.047). Patients with DR had a longer median PFS (10.1 vs. 1.5 months; p<0.0001) and OS (23.9 vs. 5.6 months; p=0.0001) than those with true PD. All patients with PsPD or DR were administrated with continuing ICIs. Among patients who experienced an initial progression (excluding patients with PsPD and DR), the continuing ICIs treatment cohort (n=20) still had a significantly longer median OS (7.5 vs. 3.1 months; p=0.004) than discontinuing ICIs treatment cohort (n=11). Conclusions: PsPD and DR are uncommon patterns of disease progression. Patients with DR exhibited a relatively favorable clinical outcome. Prognosis or biomarkers are needed to identify early patients with atypical responses who will benefit from immunotherapy.