Complete Response in Salivary Duct Carcinoma Ex Pleomorphic Adenoma With Upfront Combination of Trastuzumab and Chemo-Hormonal Therapy.

Salivary duct carcinoma (SDC) is one of the rarest malignancies. It can arise de novo or from pre-existing pleomorphic adenoma (carcinoma ex pleomorphic adenoma - CXPA) and can be very aggressive. Here, we present one such case of a 48-year-old male with relapsed, widely invasive SDC ex pleomorphic adenoma of the parotid that was locally advanced with intracranial extension that was refractory to chemo-radiation. Immunohistochemistry confirmed positivity for human epidermal growth factor receptor-2 (HER2) and androgen receptor (AR). He was started on a combination of trastuzumab, Combined Androgen Blockade (CAB) with leuprolide and bicalutamide, and docetaxel. Follow-up imaging at three months and nine months from treatment initiation demonstrated a complete response, ongoing at 17 months at follow-up. The upfront combination of anti-HER2 therapy, CAB, and chemotherapy resulted in a durable complete response in an aggressive disease. The result obtained from our experience provides valuable insight into the management of a rare and treatment-resistant entity, where large prospective studies without heterogeneity are not possible.