Sclerosing mucoepidermoid carcinoma of the salivary glands.

Mucoepidermoid carcinoma (MEC) comprises approximately 30% of all salivary gland malignancies, making it the most common malignant tumor of the salivary glands. Multiple histologic variants with a wide range of differentiation have been described. Sclerosing MEC (SMEC) is a rare subtype that may be misdiagnosed as a benign reactive condition or low-grade non-SMEC malignancy. We report 4 cases of SMEC and evaluated them with Her-2/neu and MIB-1 to determine whether an association exists between the histologic grade and immunohistochemical findings. In 3 cases, histologic examination demonstrated relatively well-circumscribed, nonencapsulated tumors composed of extensive central sclerosis with keloid-like stroma and scattered epithelial islands of low-grade MEC. In the fourth case, the tumor showed similar sclerotic stroma; but the epithelial component was of intermediate grade. In all 4 cases, eosinophils and neutrophils were part of the inflammatory infiltrate; and the edges were surrounded by lymphoid tissue, with germinal center formation and residual epithelial islands. A Mayer mucicarmine stain revealed abundant intracytoplasmic mucin. We found MIB-1 labeling indices of 5% or less in cases 1, 2, and 3 and 12% in case 4, suggesting an association between MIB-1 index and tumor grade. The tumors were negative for Her-2/neu in all 4 cases. The latter seems to bear no relationship to tumor grade.