Molecular heterogeneity in mucoepidermoid carcinoma: conceptual and practical implications.

Mucoepidermoid carcinoma (MEC), the most common salivary gland malignancy of the upper aerodigestive tract and tracheobronchial tree, is also known for its considerable cellular heterogeneity including epidermoid, intermediate and mucin producing cells. Despite this structural and cellular heterogeneity, MEC is uniquely characterized by a specific translocation t(11; 19) (q12; p13), resulting in a fusion between the MECT1 and the MAML2 genes. Although the incidence of this fusion in MEC varies, it is generally accepted that more than 50 % of this entity manifest the MECT1-MAML2. Fusion-positive cases showed significantly better survival than fusion-negative cases, suggesting that MECT1-MAML2 represents a specific prognostic molecular marker in MEC. We contend that fusion in MEC represents a distinct mechanism in the development of this entity. In that context, fusion positive MEC, regardless of grade, manifest a more stable genome and better clinical behaviour, while fusion negative MEC represent a distinctly different pathway characterized by marked genomic instability and relatively aggressive tumors.