**4.3 Tumours with clear cell and vacuolated cell pattern**

The differential diagnosis of tumours of intraoral SGs comprising of clear cells and vacuolated cell pattern include – Epithelial–Myoepithelial carcinoma (EMC), Myoepithelial tumours such as myoepithelioma (ME) and myoepithelial carcinoma (MC), clear cell carcinoma (CCC), mucoepidermoid carcinoma (MEC), acinic cell carcinoma (AciCC), secretory carcinoma (SC).

#### **Figure 9.**

*9a: Showing cells arranged in a predominant papillary architecture with fine fibrovascular core in a case of acinic cell carcinoma. The cells have fine vacuolated cytoplasm (May-Grunwald Giemsa stain x 4), 9b: Corresponding histology showing branching papillae (arrow) with fibrovascular core (Haematoxylin & Eosin x 4).*

*Cytopathology of Intraoral Salivary Gland Tumours and Tumour-Like Lesions… DOI: http://dx.doi.org/10.5772/intechopen.98872*

## *4.3.1 Epithelial–myoepithelial carcinoma (EMC)*

It is a an unusual tumour of major salivary gland predominantly occurring in parotid (60–80%) but can also be seen in minor SGS [20]. Palate is the most common site of occurrence and clinical presentation can be a ulcerative nodular lesion.

**Key cytological features –** The smears are cellular comprising of biphasic population of epithelial and myoepithelial cells. The myoepithelial cells are seen in loosly cohesive sheets, clusters and spheres with fragile, pale to clear delicate glycogen rich cytoplasm that disperses in background resulting in many naked or stripped nuclei. The nucleus of myoepithelial cells is round to oval with open chromatin and small distinct nucleoli (**Figure 10a**). Epithelial cells are seen usually in tight cohesive clusters. Sometimes mild nuclear atypia can be encountered. Hyaline stromal globules and basement membrane-like material can also be seen. The biphasic pattern of EMC can be demonstrated by using IHC on cell blocks with low molecular weight keratin and epithelial membrane antigen (EMA) for highlighting the duct cells and with smooth muscle actin (SMA), calponin, p63 and S-100 for highlighting the myoepithelial cells component [37]. Points of differentiation of EMC with other tumours with clear and vacuolated cells are discussed with each individual tumour**.**

#### *4.3.2 Myoepithelioma (ME)*

**Myoepithelioma (ME)** is a benign tumour that can occur in minor SGs with palate being the most common site. The myoepithelial cells in ME have pale to clear cytoplasm (**Figure 5b**), resembling myoepithelial cells of EMC. However, the myoepithelial cells of EMC are larger than that of ME due to presence of abundant glycogen [21]. Also, ME lacks the biphasic pattern of EMC (**Figure 10a**). ME may undergo transformation into myoepithelial carcinoma (MC). However, atypical cytological features such as nuclear pleomorphism, coarse chromatin with prominent nucleoli with background necrosis and mitotic activity seen in MC can differentiate between the two [21]. Differentiation of ME from cellular PA with predominant myoepithelial component is already discussed at 4.1.1e.

#### *4.3.3 Clear cell carcinoma (CCC)*

**Clear cell carcinoma (CCC)** of the SG is a rare low-grade malignancy that occurs primarily in intraoral minor salivary glands predominantly in the palate [38].

#### **Figure 10.**

*10a: Smear showing admixture of dual population of cells comprising of epithelial and myoepithelial cells in a case of epithelial myoepithelial carcinoma (Haematoxylin & Eosin x 40), 10b:s Smear showing a cluster of cells with multilayering of round to polygonal oncocytic cells (arrow) with round nucleus and abundant dense granular cytoplasm in a case of an oncocytoma (May-Grunwald Giemsa stain x 40)*

Epithelial cells of CCC are seen in clusters and sheets with prominent cell borders, uniform round to ovoid nuclei, granular chromatin and abundant glycogen rich clear cytoplasm**.** The cells of **CCC** may resemble myoepithelial cells of EMC. Unlike EMC, CCC lack evidence of either ductal or myoepithelial differentiation.

Clear cells can be encountered in MEC of minor SGs. However, identification of other accompanying cells (intermediate and epidermoid cells) in MEC gives clues to the diagnosis [34]. Mucin in cells of MEC can also be demonstrated by mucicarmine stain on cell blocks.
