Noninvasive carcinoma ex pleomorphic adenoma of the parotid gland: A difficult diagnosis on fine needle aspiration

Carcinoma ex pleomorphic adenoma (CXPA) is a rare epithelial malignancy that arises from a primary or recurrent pleomorphic adenoma (PA). It may be noninvasive (NI) or invasive. NI CXPA is extremely rare. Preoperative diagnosis on fine needle aspiration (FNA) of CXPA may be difficult and poses a diagnostic challenge to clinicians and pathologists. Herein, we describe the FNA findings of a case of NI-CXPA. A 69-year-old woman presented with rapid enlargement of a stable parotid mass of 25 years. Cytologically, malignant cells were focally associated with metachromatic fibromyxoid matrix that was homogeneous and dense with a vague fibrillary quality. There were cell groups, papillary-like clusters and single malignant cells. The nuclei were pleomorphic with irregularly dispersed chromatin, and the cytoplasm was ill-defined and granular. Nucleoli were small to inconspicuous. Mitoses and necrosis were not seen. Cytological features were not specific for any type of salivary gland carcinoma. The FNA diagnosis was primary high-grade adenocarcinoma of the parotid gland, not otherwise specified. Facial nerve-sparing total parotidectomy was performed, which histologically showed PA interspersed with ducts and nests composed of pleomorphic atypical nuclei surrounded by extensive hyalinization. Single cells were also noted. No capsular infiltration was seen in the entirely sampled tumor. Immunohistochemistry for Ki-67 showed a higher proliferation rate in the malignant ducts and p63 positive cells focally surrounded some of the malignant ducts. Histological diagnosis was NI-CXPA. Accurate diagnosis is important for proper surgical management; however, the preoperative diagnosis of NI-CXPA is difficult to make on FNA.