Hybrid carcinoma of the salivary gland: salivary duct adenocarcinoma adenoid cystic carcinoma.

AIMS Hybrid tumours of the salivary gland are rare neoplasms that have been described only in the parotid and palate. Their recognition is important particularly when the component tumours have different biological behaviours. The occurrence of a submandibular hybrid tumour has not been reported. METHODS AND RESULTS We describe a case of a 36-year-old woman with a hybrid carcinoma composed of salivary duct adenocarcinoma and adenoid cystic carcinoma of the right submandibular gland. There was no evidence of a pre-existing or concurrent pleomorphic adenoma. The presence of the two components was verified by differential immunohistochemical staining using a panel of cytokeratin, vimentin, smooth muscle actin and S100. The patient subsequently developed metastases to the pelvis, lumbar, vertebra and wrist. The clinical course in this patient was consistent with the behaviour of the salivary duct adenocarcinoma component. CONCLUSIONS The histogenesis of hybrid tumours is largely unknown, but in this case it may represent diverging differentiation of luminal tumour cells. Because some histological features of different salivary gland tumours overlap, immunohistochemistry is a valuable tool especially when used to delineate the components of a hybrid tumour.