Salivary Gland Cancers: Biology and Systemic Therapy

Salivary gland tumors are a relatively rare and heterogeneous group of tumors with variable pathologic and phenotypic characteristics. The lack of clinical outcomes data and randomized controlled trials pertaining to them makes it difficult to formulate definitive treatment protocols that could help with making decisions regarding choice of therapy. Most studies involving systemic chemotherapy have not shown promising patient outcome results. With recent advances in molecular technology, however, it is now possible to identify specific genetic alterations and biomarkers as possible targets for therapeutic purposes. For example, in mucoepidermoid carcinomas, one of the most common types of malignant salivary gland tumors, a commonly seen genetic translocation [t(11;19)(q21;p13), which involves the CRTC1 and MAML2 genes] has been found to be associated with improved survival, making it a possible prognostic marker. Also, this translocation gives rise to a fusion protein that appears to render tumors highly sensitive to epidermal growth factor receptor (EGFR) inhibition. However, the results of phase II trials of EGFR inhibitors-as well as other targeted agents--in salivary gland tumors have been disappointing: there has been some disease stabilization but no objective responses. There remains a need for well-designed prospective clinical studies to improve management of these tumors.