Messenger RNA levels for ras were unchanged from control levels in all tumors, while the level of src mRNA was higher in the tumor samples than the normal parotid tissue. Many cell types of the salivary glands have clear cytoplasm. Causes of clear cytoplasmic quality in light microscopy are loss of organelles, storage of substances or fixation artefacts. Differential diagnosis of the different clear cell types requires special staining techniques, immunocytochemistry and electron microscopy. A new and distinct salivary gland neoplasm is hyalinizing clear cell carcinoma, which was not included in the second edition of the WHO Classificati- on of Salivary Gland Tumors.
Most cases occur in women.
The pathohistology is characterized by solid or trabecular formations of polygonal clear cells which are surrounded by a broad hyalinized desmoplastic connective tissue stroma. The clear cells are mucin negative and express cytokeratin and EMA, in some cases also CEA, but not S-100 protein, actin or other markers of myoepithelial cells. Ultrastructural findings are undifferentiated duct cells with only few organelles and inclusion of glycogen granules. The differential diagnosis includes other clear cell tumours, especially epithelial- myoepithelial carcinoma and the clear cell variants of myoepithelial carcinoma and acinic cell or mucoepidermoid carcinoma. TI - A case report of mucoepidermoid carcinoma of the parotid gland developing after radioiodine therapy for thyroid carcinoma.