Leveraging homologous recombination deficiency for sarcoma : Unravelling homologous recombination repair deficiency and therapeutic opportunities in soft tissue and bone sarcoma.

Background: Homologous recombination deficiency (HRD) in tumors correlates with poor prognosis and metastases development. Determining HRD is of major clinical relevance as it can be treated with PARP inhibitors (PARPi). HRD remains poorly investigated in sarcoma, a rare and heterogeneous cancer of mesenchymal origin.

Objective: We aimed (i) to investigate predictive biomarkers of HRD in several independent sarcoma cohorts using a cross-functional strategy by combining genomic, transcriptomic and phenotypic approaches and (ii) to evaluate the therapeutic potential of PARPi and DNA damage response (DDR)-based therapies ex vivo.

Materials and methods: We performed a comprehensive genomic and transcriptomic characterization of sarcoma using datasets from The Cancer Genome Atlas (TCGA) and Therapeutically Applicable Research to Generate Effective Treatments (TARGET), and our own bone and soft tissue sarcoma cohorts. We evaluated PARP1/2 and WEE1 inhibition ex vivo in patient-derived sarcoma cell models as monotherapy and in combination with chemotherapeutic agents to identify synergistic effects.

Results: Firstly, we identified genomic traits of HRD in a subset of sarcomas associated with molecular alterations in homologous recombination repair (HRR) pathway genes and high chromosomal instability. Secondly, we identified and validated distinct SARC-HRD transcriptional signatures that predicted sensitivity to PARPi. Finally, we showed functional defects in HRR in sarcoma cells that were associated with functional dependency towards PARPi and WEE1i and support the clinical use of RAD51 as a predictive biomarker for PARPi sensitivity.

Conclusion: We provide a personalized oncological approach to potentially improve the treatment of sarcoma patients. We encourage the evaluation of gene expression signatures to enhance the identification of patients who might benefit from DDR-based therapies.