Objective: The purpose of this study was to examine the prognostic impact of HER2 expression and anti-HER2 therapy in parotid salivary duct carcinoma （SDC） and invasive carcinoma ex-pleomorphic adenoma （iCXPA）.
Subjects and Methods: The subjects of this study were 25 SDC and 15 iCXPA patients initially treated between 2002 and 2022 at the Department of Otorhinolaryngology and Head and Neck Surgery, Osaka Medical and Pharmaceutical University. The study included HER2 expression and clinical background, recurrence rate, clinical course of 9 patients treated with anti-HER2 therapy at the time of recurrent metastasis, and adverse events.
Results: HER2-positive cases had more lymph node metastases than negative cases. Twenty-one of 34 patients who underwent initial radical surgery relapsed. The response rate to anti-HER2 therapy was 66.7％, CR rate was 33.3％, 1-year disease control rate was 76.2％, and 5-year disease-specific survival rate was 87.5％. The median progression-free survival was 18 months. Among HER2-positive patients, those treated with anti-HER2 therapy had a significantly better prognosis than those not treated with anti-HER2 therapy （p＝0.01）.
Discussion: HER2-positive patients with unresectable or distant parotid adenocarcinoma may have a good chance of long-term survival with anti-HER2 therapy. However, anti-HER2 therapy is less effective for intracranial metastases and requires periodic imaging evaluation. Further investigation of the efficacy of adjuvant anti-HER2 therapy for HER2-positive parotid cancer is warranted.