Efficacy of S-1 Monotherapy for Salivary Duct Carcinoma With MYC Amplification

BACKGROUND/AIM: Salivary duct carcinoma (SDC) is a rare, highly aggressive subtype of salivary gland carcinoma, commonly characterized by overexpression of erb-b2 receptor tyrosine kinase 2 [ERBB2, commonly known as human epidermal growth factor receptor 2 (HER2)] and androgen receptor positivity. Anti-HER2 therapy, platinum-based chemotherapy, and androgen-deprivation therapy (ADT) are commonly provided as standard systemic treatments for advanced SDC; however, effective therapeutic options after failure of these treatments remain limited. The clinical efficacy of S-1 monotherapy in SDC and its predictive biomarkers are not well established. Herein, we present a case in which S-1 monotherapy showed efficacy in a case of SDC after resistance to anti-HER2 therapy, platinum-based chemotherapy, and ADT. CASE REPORT: ). S-1 monotherapy was started as a late-line therapy. Computed tomography scans 2 months later showed shrinkage of lung and liver metastases, with disease control maintained for more than 5 months. CONCLUSION: amplification.