The cellular pleomorphic adenoma demonstrates a tan-white, bulging glistening cut surface with lobulations. Note that the tumor is well-circumscribed.
A solid proliferation of basaloid cells in this cellular pleomorphic adenoma may be virtually indistinguishable from basal cell adenoma. One must look for more typical areas of pleomorphic adenoma to make the distinction.
The cellular component forms trabeculae, and one can see a hint of the mesenchymal component interspersed -- note the patches of bluish myxoid stroma in the right bottom image.
Like all pleomorphic adenomas, the cellular variant is well-circumscribed and encapsulated.
The cells show vesicular chromatin and a moderate amount of cytoplasm.
Corresponding FNA shows these cells appear slightly more crowded than the usual pleomorphic adenoma.
A different case shows cellular growth of cells without intervening stroma at all.
One slide did harbor distinct stromal areas of myxoid change revealing the accurate nature of this tumor.
Pleomorphic adenomas are the most common benign tumor of the salivary glands. For a full discussion on these tumors, please visit our case of this entity (see link below). This will simply be a brief discussion on the cellular variant.
The composition of pleomorphic adenoma consists of three main components: (1) epithelial cells lining the ductal or glandular structures; (2) myoepithelial cells enveloping the ductal cells and also forming sheets, nests and single cells in the matrix; (3) a chondromyxoid stroma. Tumors with very scanty or even absent stroma are called cellular pleomorphic adenomas. Some authors suggest that stroma-rich variants of PA are more likely to recur, whereas the cellular variants of PA are more likely to undergo malignant transformation.1
It is important just to keep in mind that this cellular variant exists to avoid overdiagnosing it as a malignant tumor. Furthermore, cellular pleomorphic adenoma may be difficult to distinguish from basal cell adenoma, however, thorough sampling should reveal more characteristic areas in a pleomorphic adenoma.
1 Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 244-252.