Carcinoma ex pleomorphic adenoma: A diagnostic challenge on cytology.

Carcinoma ex pleomorphic adenoma (Ca ex PA) is a malignant neoplasm arising from primary or recurrent benign pleomorphic adenoma. It is rare with an annual incidence rate of 0.17 tumors per million. Histopathology remains the gold standard for the diagnosis of Ca ex PA, with only a handful of cases reported on cytology. In our case a 66-year-old male presented with the right parotid mass for 5 years rapidly increasing for the last 3 months. Fine needle aspiration cytology (FNAC) smears showed malignant tumor cells in clusters along with benign myoepithelial cells in chondromyxoid background. Histopathologically, highly pleomorphic malignant epithelial cells in sheets along with foci of comedonecrosis and areas corresponding to benign pleomorphic adenoma were observed on careful scrutiny. Immunohistochemistry revealed positivity for cytokeratin (CK 7) and gross cystic disease fluid protein 15 (GCDFP-15) while CK5/6 and high molecular weight CK (34 βE12) were negative in the malignant tumor cells. So, the final impression was Ca ex PA with salivary duct carcinoma as malignant component. We hereby report this case to highlight the significance of FNAC in the diagnosis of Ca ex PA which can be easily missed on cytopathology. However, it is important to corroborate the cytological findings with clinical suspicion of malignancy as well as radiology. Diagn. Cytopathol. 2017;45:651-654.