In this issue of Clinical Cancer Research, Okabe et al.(1) have analyzed 71 cases of mucoepidermoid cancer and 51 cases of non-mucoepidermoid cancer for the presence of the Mect1-Maml2 fusion oncogene and have made a valuable observation. They confirmed that Mect1-Maml2 expression is specific for mucoepidermoid cancer and showed that fusion-positive tumors have histologic and prognostic features that are strikingly distinct from fusion-negative tumors. Although these data raise important points for both the diagnosis and management of these patients, it is helpful to first review the recent findings that have led to this retrospective clinical study.

Malignant salivary gland tumors represent a heterogeneous collection of cancers, which, due to their low incidence in the population, have often been grouped together (2). Accordingly, there has been little progress in defining the prognosis and treatment for these distinct neoplastic diseases. For example, although mucoepidermoid cancer is the most common malignant salivary gland tumor, there had been few insights into the genetic or biological basis of this tumor in the 100 years since it was first described by Volkmann in 1895 (3). In 1945, Stewart et al. established the term ‘‘mucoepidermoid’’and defined this neoplasm as a specific pathologic entity under the designation of ‘‘tumor’’due to its often benign but unpredictable clinical behavior (4). Only in 1953 did Foote and Frazell establish the term mucoepidermoid carcinoma, considering them all as malignant lesions (5). It was also recognized at this time that a characteristic histologic feature of mucoepidermoid cancer was the presence of varying amounts of three different cell types designated as epidermoid cells, mucin-producing cells, and intermediate cells. The relative amounts of epidermoid and mucinproducing cells, as well as the degree of cyst formation and cell differentiation, subsequently allowed for a prognostic classification of mucoepidermoid cancer, which could be scored as grades 1 to 3 (6), or as low-grade, mid-grade, and high-grade tumors (7). Although Okabe et al.(1) used a