Homologous recombination repair deficiency as a therapeutic target in sarcoma

Sarcoma is a rare cancer arising from soft tissue and bone and consists of more than 50 distinct subtypes. There is an increasing emphasis on understanding the cancer biology of individual sarcoma subtypes to inform the development of targeted and immunotherapy-based treatment approaches. While some advances have recently been made in this respect, most sarcomas are still treated with chemotherapy. The homologous recombination DNA repair pathway plays an important role in repairing highly cytotoxic double-stranded DNA breaks and restarting stalled replication forks. A subset of human cancers, notably ovarian, breast, prostate, and pancreatic cancers, harbor defects in components of the homologous recombination repair pathway, such as mutation or loss of BRCA1/2, and are sensitive to treatments which induce double stranded DNA breaks or replication fork arrest, including oral small molecule poly-ADP-ribose polymerase (PARP) inhibitors. Our understanding of DNA repair defects in sarcoma remains at an early stage. Recently, uterine leiomyosarcoma was identified as a sarcoma subtype with characteristic defects in the homologous recombination repair pathway and frequent BRCA2 loss. Preclinical data, presented here, demonstrates marked activity for the PARP inhibitor olaparib in combination with the alkylating agent temozolomide in leiomyosarcoma models. Ongoing research promises to identify other sarcomas with DNA repair defects and may offer a new opportunity for the targeted treatment of this rare, aggressive cancer.