Clear-Cell myoepithelial carcinoma of the salivary glands: A clinico-pathologic, immunohistochemical, and ultrastructural study of two cases involving the submandibular gland with review of literature

Myoepiythelial carcinoma (MC) is an uncommon neoplasm of the salivary glands, and cases of the clear-cell (CC) variant are extremely rare. Two cases of MC of the CC variant arising in the left submandibular gland are described herein. Both cases, which involved elderly women, almost exclusively consisted of large glycogen-rich CCs. Both cases were immunopositive for several epithelial and myoepithelial markers, and electron microscopy (EM) demonstrated hybrid epithelial and myoid differentiation in both. Case 1 arose in a pre-existing pleomorphic adenoma ( "ex mixed tumor MC" ), while case 2 was a "de novo MC". CC-MC is an aggressive tumor with frequent recurrence, lymph node, and systemic metastases. A total of 14 cases of this type of neoplasm have been reported so far in the salivary glands, two arising from the submandibular gland. To date, only four cases have been studied using the EM. The cases of CC-MC presented here are the third and the fourth ones, respectively, originating from the submandibular glands,and the first two cases arising from this location, in which EM investigation succeeded in demonstrating myoepithelial differentiation. CC-MC needs to be distinguished from diverse primary and secondary CC neoplasms.