Title: HER2-Positive Salivary Duct Carcinoma: A Case of Durable Response to Targeted Therapy and Chemotherapy

Salivary Duct Carcinoma (SDC) of the parotid gland represents a rare and aggressive malignancy. Standard treatment for metastatic SDC involves cytotoxic chemotherapy including platinum and taxane based agents. Notably, a subset of these carcinomas are characterised by over expression of the human epidermal growth factor receptor 2 (HER2) which is associated with an aggressive metastatic phenotype. While trastuzumab-based therapies have shown promise in the management of metastatic HER2-positive SDC, the incorporation of pertuzumab, a HER2 dimerisation inhibitor, represents a novel therapeutic approach. This case describes a 56 year old patient with metastatic parotid carcinoma ex-pleomorphic who experienced sustained complete reponse with the addition of pertuzumab to a carboplatin, paclitaxel and trastuzumab regime.This case underscores the importance of testing for HER2 expression in SDC and highlights the potential therapeutic benefit of incorporating anti-HER2 targeted therapies, including pertuzumab, into the management of patients with HER2-positive disease. Further prospective research is warranted to validate the role of pertuzumab in this context and to establish its integration into standard treatment protocols.