Targeted Approaches Applied to Uncommon Diseases: A Case of Salivary Duct Carcinoma Metastatic to the Brain Treated with the Multikinase Inhibitor Neratinib

Salivary duct carcinoma is a rare malignancy associated with hormone receptor and human epidermal growth factor receptor 2 (HER2) overexpression. Local surgical control is the cornerstone of therapy, but a subset of patients develops metastatic disease portending a poor prognosis and limited management options. Intracranial metastases are an uncommon manifestation and present a therapeutic challenge. We report the case of a 31-year-old male who presented with facial pain and swelling subsequently diagnosed with salivary duct carcinoma. Our patient underwent extensive locoregional resection and analysis of the tumor tissue demonstrated evidence of androgen receptor expression and HER2 overexpression. His course was complicated by metastatic extra- and intracranial recurrence despite combined modality treatment with radiation and chemotherapy followed by anti-HER2 monoclonal antibody therapy and androgen deprivation therapy. After exhausting standard treatment options, he received experimental therapy with a new small-molecule tyrosine kinase inhibitor, neratinib, with evidence of a transient clinical response and no significant adverse effects. This case exemplifies the potential and limitations of targeted therapy, particularly when applied to patients with rare diseases and presentations.