Molecular differences in mucoepidermoid carcinoma and adenoid cystic carcinoma of the major salivary glands

Objective/Hypothesis. Mucoepidermoid carcinoma (MEC) and adenoid cystic car cinoma (ACC), the most common malignancies of the major salivary glands, ar e clinically and pathologically different. To determine whether MEC and ACC have different molecular characteristics, we examined the expression of er bB-2, erbB-3, epidermal growth factor receptor (EGFR), and transforming gro wth factor-alpha (TGF-alpha), important molecular features in other maligna ncies. Study Design/Methods. Archival tissue sections of 22 MEC and 6 ACC t umors of the major salivary glands were evaluated immunohistochemically for expression of erbB-2, erbB-3, EGRF, and TGF-alpha. A differential immunost aining score, reflecting the difference in immunostaining between carcinoma and uninvolved salivary gland tissue, was calculated for cytoplasmic and m embranous staining. Results. Positive immunostaining for all biomarkers was observed in the cytoplasm and membrane of both tumors. However, expression was higher in MEC than in ACC tumors and was statistically significant for cytoplasmic EGFR (P =.009), TGF-alpha (P =.041), and membranous EGFR (P =. 004). A significantly higher percentage of MEC cells also demonstrated posi tive immunostaining for cytoplasmic erbB-3 (P =.022), EGFR (P =.005), membr anous erbB-3 (P =.022), and EGFR (P =.013). The differential immunostaining score was significantly higher for MEC compared with uninvolved alveolar t issue and the membranes of uninvolved ductal tissue. There were no statisti cally positive differential immunostaining scores for ACC. Conclusions. The re is a clear difference in the molecular phenotypes of MEC and ACC. The la ck of statistically significant expression in ACC, when compared with simil ar uninvolved. salivary gland tissue, suggests minimal involvement for thes e molecular structures in the pathogenesis of ACC. Conversely, erbB-2, erbB -3, EGFR, and TGF-alpha may have a role in the development and progression of MEC. These results have therapeutic implications for MEC of the major sa livary glands.