Salivary duct carcinoma: A case report of oncocytic variant with possible treatment implications and review of literature.

Salivary duct carcinoma (SDC) is an aggressive malignancy, resembling high-grade ductal carcinoma of the breast. Histologically, it shows cords and nests with cribriforming, marked nuclear atypia, comedonecrosis, perineural, and lymphovascular invasion. We report a rare case of SDC in a 61-year-old woman presenting with facial asymmetry, dysphagia, and cervical lymphadenopathy. Imaging showed an ill-defined infiltrating mass in parotid gland and multiple enlarged cervical lymph nodes. Histologically, the largest focus of tumor consisted of an intra-parotid lymph node replaced by sheets of bland appearing oncocytic tumor cells with abundant cytoplasm, centrally placed nucleus, and single prominent nucleolus. No mitotic figures were identified and focal areas showed nests with comedonecrosis and desmoplastic stromal response. Tumor showed strong positive staining for androgen receptor, CK7 and GATA-3. In addition, tumor stained strong positive for Her2neu making the patient amenable to Herceptin. NGS detected mutation in HRAS (p.Q61R) and a novel, not previously reported mutation in PIK3CA, (exon 21, p.H1047L). This case represents a rare presentation of SDC with bland cellular morphology unlike the usual associated high grade features. In addition, it reemphasizes the importance of androgen receptor in differential diagnosis from its mimics like oncocytic carcinoma and oncocytic variant of mucoepidermoid carcinoma. Further, Her2neu immunohistochemical status can be used for diagnosis as well as guide targeted therapy in these aggressive tumors.