LAUSR

Background New patterns of progression under immune-oncology (IO) antibodies (mAb) have been described such as pseudoprogression. Except for melanoma, variations between studies reveal difficulties to establish their prevalence. Methods This retrospective study enrolled patients participating in IO phase I trials at Gustave Roussy cancer center for solid tumors excluding melanoma. Radiological assessment according to iRECIST was correlated with prospectively registered patient characteristics and outcomes. Pseudoprogression (PsPD) was defined as RECIST-defined progression followed by stabilization or decrease at the next imaging, and dissociated response (DisR) as concomitant decrease in some tumor lesions and increase in others at a same timepoint. Results Among 360 patients included, 74% received IO mAb combination: 45% with another IO mAb, 20% with targeted therapy and 10% with radiotherapy. The overall response rate was 19.7%. PsPD were observed in 10 (2.8%) patients and DisR in 12 (3.3%) patients. Atypical responses (AR), including PsPD and DisR, were not associated with any patient’s baseline characteristics. Compare with typical responder patients, patients experiencing AR presented a shorter iPFS (HR 0.34; p  < 0.001) and OS (HR 0.27; p  = 0.026). Among the 203 patients who progressed in 12 weeks, 80 (39.4%) patients were treated beyond progression. PD was confirmed in 80% of cases, while 10% of patients presented a response. Conclusion Pseudoprogression and dissociated response are uncommon patterns of progression. Their prevalence should be balanced with the rate of real progressing patients treated beyond progression. Prognosis or on-treatment biomarkers are needed to identify early patients who will benefit from immunotherapy.