Supplementary Material for: Metastatic Salivary Duct Carcinoma with ERBB2 Amplification and Sequential Response to Ado-Trastuzumab Emtansine and Neratinib: A case report

Introduction: Salivary duct carcinoma (SDC) is an aggressive and rare subtype of salivary gland carcinomas. Surgical excision and radiotherapy are standard of care for early cancer. Chemotherapies with taxanes and platinum show overall response rates between 39% and 50%. SDC are often associated with an overexpression of the androgen receptor (AR) and HER2/neu which have recently become druggable targets. Case Presentation: Here we report on an 84-year-old male patient with metastatic SDC of the right parotid gland. In 2017, he underwent a right total parotidectomy, a right neck dissection and an infratemporal fossa clearance followed by six weeks of radiotherapy. In 2018, due to metastatic spread in the lungs, bones and pararenal gland, a pathological work up of the tumor tissue was performed and revealed both AR and HER2 overexpression, respectively. Consequently, he underwent androgen deprivation therapy (ADT) and, due to asymptomatic progression, sequentially HER-2-targeted therapy with ado-trastuzumab emtansine and neratinib, which led to stable disease during the course of about 18 months. Electronically captured patient reported outcome (ePRO) had demonstrated a good tolerance of all three therapeutic lines. Conclusion: In conclusion, since effective standard therapeutic treatment options for SDC may often not be tolerable in older patients, the implementation of personalized and adaptive treatments especially in patients with rare tumor types might offer valuable treatment options.