(P 77) MULTI-PARAMETRICAL PROFILING OF CHONDROSARCOMA

Objective: Chondrosarcomas (ChS) are considered “cold” tumors due to their poor response to immunotherapy. Treatment of these tumors is limited to surgical resection, and effective systemic therapies are lacking. The molecular biology and immunophenotype of ChS, as well as their role in disease progression, are still poorly understood. The aim of this study was the multi-parametrical characterization of ChS to define its molecular and immune profiles. The study also aimed to identify new potential prognostic factors and select patients who may benefit from targeted or immune-therapies.

Methods: We enrolled 99 patients diagnosed with primary ChS (including 28 G1, 37 G2, 24 G3, and 10 dedifferentiated cases). To evaluate immune cell infiltrates, tissue microarrays were prepared from the central and peripheral regions of the tumors using formalin-fixed paraffin-embedded tissue blocks. The immunohistochemical (IHC) analysis included 20 markers identifying, e.g. effector T cells, B cells, antigen-presenting cells, immature/mature dendritic cells, M1/M2 macrophages, exhausted T cells, and PD-L1 expression on tumor cells. The molecular profile and tumor mutational burden (TMB) were obtained by targeted next-generation sequencing of 409 genes. Additionally, microsatellite instability (MSI) was analyzed. Fisher exact test with Benjamini-Hochberg multiple-testing correction was used for comparison between categorical variables. The overall survival (OS) rate was estimated using the Kaplan-Meier method. Multiparametric analysis was performed using LASSO-based Cox regression.

Results: The median OS of all patients was 64.6 (95% CI: 44.2 -) months. Based on clustering of IHC data, we obtained 3 clusters corresponding to different immunological phenotypes: “cold”, “hot”, and “intermediate”. The immunophenotypes were significantly differently distributed between ChS subtypes (p< 0.001). The proportion of the “cold” phenotype decreased along with histological grade, opposite to the “hot” phenotype. Molecular analysis showed that the median TMB was 2.35 mutations/Mb and none of the patients had MSI. The most frequent mutations occurred in IDH1/2 (41% of cases) and TP53 (16%) genes. These mutations were significantly correlated with tumor grade (FDR < 0.05), with prevalence in high grade ChS. The largest number of genetic alterations were identified in ChS G3, including loss of the tumor suppressor gene - TP53 and amplifications in genes encoding tyrosine kinase receptors - STK1 and AKT2. RTK-signaling, genome integrity, and chromatin histone modification pathways were the most frequently deregulated. Genetic abnormalities (especially gene loss/amplifications) related to those pathways were prevalent in the “hot” immune phenotype. In multivariate analysis, the presence of “hot” phenotype (HR: 3.36, CI:1.12-10.1, p< 0.05) or IDH1 mutations (HR: 3.34, CI:1.56-7.2, p< 0.01) predicted worse survival in ChS patients.

Conclusion: Both gene mutations as well as immunological profile play a significant role in ChS pathobiology. Pathways related to epigenetic modifications of histones, cell cycle regulation and kinase pathways may play a significant role in the development of ChS. The poor prognosis of patients with a “hot” immunophenotype may be related to overexpression of galectin-9 on T-cells. The presence of IDH1 mutations is promising ChS prognostic factor. The presented results suggest that the use of immunotherapy combined with IDH1 inhibitors may have potential as a future therapy for selected patients.