Answer: Low grade mucoepidermoid carcinoma

Histology: The tumor is composed of well formed cystic spaces of variable size lined by a mixture of mucus, intermediate and epidermoid cells. The cysts are surrounded by fibrosis, inflammation and giant cell reaction. The tumor is seen within the parotid tissue and approaching the skin dermis.

Discussion: The lesion represents a low grade mucoepidermoid carcinoma (MEC) of the parotid. MEC is the most common primary malignant tumor in adults and children. The tumor is composed of multiple cell type seen in variable proportion (mucous, epidermoid, clear, intermediate, columnar and maternal cells). Multiple grading systems have been used and usually lesions are classified as low, intermediate or high grade depending on the presence of cystic vs. solid areas and the types of cells identified. Although grade is an important prognostic factor, clinical stage however is a better prognosticator. One study showed that when a discrepancy existed between the grade and stage of the tumor (high grade, stage I or low grade, stage III) the outcome was in influenced more by the stage than the grade.

Reference(s):
– Salivary Mucoepidermoid Carcinoma: Revisited. Mario A. Luna. Adv Anat Pathol 2006; 13:293-307.