Complete Response to Trastuzumab-Based Chemotherapy in a Patient with Human Epidermal Growth Factor Receptor-2-Positive Metastatic Salivary Duct Carcinoma ex Pleomorphic Adenoma
A 74-year-old man noticed a hard, painless mass in his right parotid gland 2 months before his initial visit to our institution. His past medical history included prostate cancer, which was treated with definitive radiotherapy 2 years and 8 months ago. There was no evidence of facial nerve paralysis. Fine-needle aspiration biopsy findings of the parotid mass were consistent with those of CXPA. Positron emission tomography (PET)-computed tomography (CT) revealed an enhanced mass in the right parotid gland, without enlarged cervical lymph nodes. A total right parotidectomy along with right neck dissection and facial nerve reconstruction using cervical nerves was performed. Macroscopically, the tumor measured 25 × 17 mm at its largest dimensions and had a cartilage-like whitish cut surface with focal invasion of the surrounding fat tissue (fig. ). The mass consisted of broad hyaline tissue with nests of tumor cells (fig. ). At least two tissue components were identified: high-grade carcinoma with a cribriform growth pattern and comedo-like necrosis in the nests and slit-like tubular epithelium with myoepithelial cells at the base (fig. ). CXPA with a predominant SDC component was diagnosed on the basis of the presence of a cartilaginous, hyaline, nodular background and benign pleomorphic adenoma in the nodule.\nCT performed 4 months after a radical surgery revealed recurrence in the right cervical nodes, which was treated by right neck dissection. The recurrent tumor was histologically diagnosed as SDC (fig. ). The primary tumor was positive (score 3+) for membrane-localized HER2/neu protein (Dako, HerceptestTM) (fig. ). Dual-color chromogenic in situ hybridization revealed that HER2 gene was highly amplified (Ventana, INFORM HER2 Dual ISH) (fig. ). Five months later, CT revealed multiple bilateral pulmonary metastases (fig. ), and systemic treatment with paclitaxel (175 mg/m2) and trastuzumab (8 mg/kg dose loading followed by 6 mg/kg every 3 weeks) was initiated every 21 days. All pulmonary metastatic lesions had regressed after 4 treatment cycles (fig. ), and CR was confirmed after 7 cycles. The patient was maintained on trastuzumab alone (6 mg/kg every 3 weeks), and no evidence of disease progression was observed at the last contact with the patient, which was approximately 13 months after initiation of therapy.