Salivary duct carcinoma with heterotopic ossification in the parotid gland: A case report.

Salivary duct carcinoma (SDC) is one of the most aggressive salivary gland carcinomas. Heterotopic ossification (HO) is the formation of mature bone in non-skeletal tissues. HO can occur in a number of neoplastic lesions. However, its occurrence is markedly rare in salivary gland neoplasms and to the best of our knowledge, SDC with HO has not yet been reported. Therefore, the present report describes the first reported case of SDC with HO in the parotid gland and reviews the clinicopathological features of salivary gland neoplasms with HO. A 38-year-old Japanese male presented with a mass in the left parotid region. Physical examination revealed a poorly mobile mass, measuring 2 cm, in the left parotid gland. Total left parotidectomy was performed. A number of metastases were observed in the bone and brain, despite postoperative anti-HER2 combination chemotherapy. Histopathological examination of the resected parotid gland tumour revealed invasive neoplastic growth comprising cribriform and papillary proliferations. These neoplastic cells exhibited a rich eosinophilic cytoplasm and large nuclei containing conspicuous nucleoli. In addition, the present report outlines peculiar finding in the presence of mature bone tissue within the tumour. Accordingly, a diagnosis of SDC with HO was made. Despite the detailed mechanisms underlying the occurrence of HO in salivary gland neoplasms remaining unclear, neoplastic myoepithelial cells may serve a role in the development of HO in pleomorphic adenoma and carcinoma ex pleomorphic adenoma. However, SDC exhibited no myoepithelial cell components, therefore the mechanism of HO in SDC may differ from that in PA.