Locally advanced mammary analogue secretory carcinoma of the parotid gland

Mammary analogue secretory carcinoma (MASC) has recently been recognized as a salivary gland tumour that is characterized by the ETV6-NTRK3 fusion gene. A case of locally advanced MASC of the parotid gland in a 67-year-old man is presented here. The patient visited the hospital due to a large right infra auricular mass, which had been enlarging gradually over a period of 2 years. Contrast-enhanced computed tomography (CT) demonstrated a multilocular mass, 75 x 63 mm in size, containing a fluid component with non-uniform contrast effects in the interior portion. The mass had invaded the orbit, skull base, and parapharyngeal space. The patient had neither lymph node nor distant metastasis. The tumour showed tubular and ductal proliferation lined by a single layer of neoplastic cuboidal cells with clear foamy cytoplasm. Characteristic hobnail cells were observed. Expression of ETV6-NTRK3 fusion transcript in the tumour tissues was confirmed by RT-PCR. The final diagnosis was MASC (T4bN0M0, stage IVB). The patient received cetuximab together with radiotherapy at a total dose of 66 Gy. After treatment, CT showed a slightly reduced tumour volume, indicating stable disease. More than 56 months after treatment, the patient remains alive with no remarkable change in the tumour.