Salivary gland cancer in the era of immunotherapy: can we exploit tumor microenvironment?

Salivary gland cancers (SGCs) consist of a rare family of neoplasms with varying histology and biological behavior. Therapeutic regimens have been relatively unchanged for decades. The recent successes of immunotherapy have raised hopes for the development of more effective strategies in SGC, thus emphasizing the role of tumor microenvironment (TME) in the design for more effective therapies.

This review presents an overview of the current knowledge on the pathobiology of SGC TME and discusses the potential of immunotherapeutic targeting.

Most data on the role of TME in SGC carcinogenesis are derived from preclinical studies. Signaling cascades of immunotherapeutic interest, PD-1/PD-L1 and PD-1/PD-L2, are active in many SGCs and might be associated with biological behavior and prognosis. Immunotherapeutic attempts are very limited, but recent findings in other tumors on the role of exosomes and PD-L2 signaling suggest that TME of SGCs warrants further research, emphasizing larger cohorts, histology-based stratification, and standardized evaluation of immunomodulatory molecules, to explore the potential of targeting tumor stroma and its signaling cascades. Furthermore, combination of immunotherapies or immunotherapies with the antineoplastic agents targeting AR, HER2, and tyrosine kinases, recently introduced in SGC treatment, constitutes a promising approach for the future.