Abstract 744P
Background
The outcome of the immune checkpoint inhibitor (ICI) for treating relapsed/ refractory (R/R) osteosarcoma remained dismal. The possibility of adding stereotactic body radiation therapy (SBRT) as an immune immunostimulatory partner to osteosarcoma immunotherapy has yet to be explored.
Methods
We retrospectively reviewed patients(Pts) with R/R osteosarcoma (n=62) receiving PD-1 blockade, including ICI-only (n=21), ICI+non-SBRT radiotherapy (n=23) and ICI+SBRT (n=18) in our institution from Jan.2020 to Dec.2023. The therapeutic efficacy, safety profile as well as potential abscopal effect was explored. The peripheral immune cell cytometry as well as tumor samples were also analysed for the potential biomarker of the responder/ abscopal effector.
Results
We noticed a remarkably improved PFS of 6.03 mo in ICI+SBRT Pts, compared to ICI-only (2.13 mo) and ICI+non-SBRT (3.37 mo) Pts. The median overall survival of Pts treated with ICI+SBRT (12.0 mo) was significantly greater than ICI-only (6.9 mo) or ICI+non-SBRT(7.4 mo). Local control of radiated lesion was 8.1 mo in ICI+non-SBRT and not reached in ICI+SBRT group. Interestingly, the non-radiated lesions demonstrated better radiological response of (abscopal effect) in ICI+SBRT Pts, compared to ICI+non-SBRT. In 8 patients, repetitive (2 to 3 rounds) SBRT was delivered to the oligo-progressed lesion as a constant immunostimulator without changing the ICIs, and the second PFS post-PD reached 4.5 mo. Grade 3-4 toxicity includes pneumonitis (n=4), bronchopleural fistula (n=1). Based on tumor samples following ICI-SBRT, we found a higher immune infiltration to the tumor bed. Interestingly, baseline peripheral CD3 levels and neutrophil-lymphocyte-ratio (NLR) were predictive of the abscopal effect.
Conclusions
Our report was the first evidence of SBRT combined with ICI as an attractive combination strategy for the immunotherapy in R/R osteosarcoma.
Clinical trial identification
NA
Editorial acknowledgement
Legal entity responsible for the study
Shanghai Jiaotong University, Ruijin Hospital.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.