Diagnosis of mammary analogue secretory carcinoma of the parotid gland by cytology material: Case report of a rare tumor and a brief review of the literature

Mammary analogue secretory carcinoma (MASC) is a low-grade malignant tumor of the salivary glands that is often mistaken for other tumors. MASC also displays similar characteristics of mammary secretory carcinoma, including the gene fusion of ETV6-NTRK3. The confirmed location of MASC as a primary tumor of the salivary gland makes the distinction from mammary secretory carcinoma. 
MASC most commonly presents as a painless, slow-growing mass, most often in the parotid gland. Although complete surgical resection results in a good prognosis, more aggressive variants with metastatic potential are reported. The radiologic and clinical presentation is often nonspecific and can resemble benign lesions, thus necessitating tissue diagnosis with immunohistochemistry (IHC) and molecular studies. Our case illustrates that fine-needle aspiration (FNA) cytology material alone can provide a definitive diagnosis of MASC and a management plan. 
The typical cytohistomorphologic features are evident in adequately sampled FNA material, and IHC usually shows S-100 and mammaglobin expression and DOG-1 negativity. The final confirmation is reached through the detection of the ETV6-NTRK3 fusion gene through FISH. This case highlights the importance of a multimodal diagnostic strategy, which allows confirmation of the diagnosis of MASC with high reliability using FNA cytology and ancillary studies. The identification of the ETV6-NTRK3 translocation not only confirms the disease but also provides an opportunity for therapeutic targeting. Surgical resection with clear margins is the primary treatment, which provides long-term disease-free survival in most patients with no adjuvant therapy. We have noted how preoperative FNA cytology can help in making the best surgical decisions and providing good outcomes.