Turning 'Cold' tumors 'Hot': immunotherapies in sarcoma

Immunotherapies have an established role in the management of several advanced malignancies. Their responses are largely dependent on the presence of PD-L1, microsatellite instability (MSI), and high tumor mutation burden. Sarcomas are heterogenous tumors which comprise over 100 subtypes. They are broadly considered immunologically inert or "cold". Immunotherapy as monotherapy has shown interesting responses in a certain handful of subtypes, such as undifferentiated pleomorphic sarcoma, dedifferentiated and pleomorphic liposarcoma, and alveolar soft part sarcoma. However, the mechanisms of action of immunotherapy agents in several sarcoma subtypes remains unknown. Several sarcoma types such as leiomyosarcoma have been shown to have an immunosuppressive microenvironment. Early clinical studies suggest the emergence of B cell infiltration in sarcoma tumor tissues as well as the role of PD-1 and PD-L1 as biomarkers of response. Immunotherapy combinations with conventional chemotherapies, radiation therapies, tyrosine kinase inhibitors and oncolytic viruses are showing promise in turning these "cold" tumors "hot". Several novel agents as well as repurposing therapies with the potential to enhance immunotherapy responses are undergoing pre-clinical and clinical studies in other tumor types. Herein we review current clinical studies which have explored the use of immunotherapeutic agents in the management of sarcomas and discuss the challenges and future directions.