Synchronous mandibular squamous cell carcinoma and parotid gland salivary duct carcinoma ex-pleomorphic adenoma: A case report

The upper gastrointestinal and respiratory tracts are the most common sites of synchronous cancers associated with oral squamous cell carcinoma (OSCC). To the best of our knowledge, synchronous OSCC and salivary duct carcinoma ex-pleomorphic adenoma (SDC ex-PA) have not been reported. A 51-year-old Japanese man was referred to our hospital with a complaint of dull pain in the mandible. He had been under observation for parotid mass that had not changed in size for 20 years. Contrast-enhanced magnetic resonance imaging revealed a 49 x 42 mm mandibular tumor and a 35 mm mass in the parotid gland with relatively well-defined borders. The left upper jugular and submandibular lymph nodes were enlarged. The clinical diagnosis was mandibular carcinoma (T4bN2bM0) and suspected pleomorphic adenoma. The patient was treated by tracheotomy, modified radical neck dissection, hemi-mandibulotomy, parotid tumor enucleation, and free fibula flap reconstruction under general anesthesia. The histopathology findings revealed that the mandibular tumor contained multilobed tumor cells that infiltrated and proliferated like foci. Tumor foci in the parotid gland were dispersed throughout the hyalinized stroma. The tumor cells had abundant and acidophilic cytoplasm, as well as nuclei of varying sizes and morphologies. Immunohistochemical staining revealed that the parotid tumor was positive for androgen receptor, human epidermal growth factor receptor type 2 and gross cystic disease fluid protein-15. The pathological diagnosis was well-differentiated SCC of the mandible (pT4bN0M0) and SDC ex-PA of the parotid gland (pT3N0M0). The surgical margin of parotid gland carcinoma was insufficient and required adjuvant chemoradiotherapy. The patient has remained disease-free for 2.5 years.