A 46 year old man with a superficial parotid mass
Christine James, D.O., Kymberly Gyure, M.D., and Matthew Smolkin, M.D.
A 46 year old man with a past medical history of hypertension, coronary artery disease, aortic valve replacement and a 45 pack-year smoking history presented to otolaryngology with a six month history of a slowing enlarging right preauricular mass. A CT scan done at an outside facility showed a 1.7 x 1.3 x. 1.2 cm superficial parotid mass without lymphadenopathy.
A fine needle aspiration of the neck mass was done at an outside facility and showed a hypercellular specimen with dispersed and loosely cohesive cells with finely to coarsely vacuolated cytoplasm. Zymogen granules were not identified. The patient subsequently underwent a right superficial parotidectomy with facial nerve monitoring.
The excisional biopsy revealed a well-circumscribed, focally hemorrhagic, yellow, lobulated mass (Figure 1).
Microscopy revealed solid and papillary architecture. The monomorphic cells have large, round nuclei with prominent nucleoli and markedly vacuolated cytoplasm. Intraluminal, amphophilic secretions and occasional psammoma bodies are present (Figures 2-4). The cells are positive for vimentin and weakly positive for GATA3 (Figures 5-6). The lesion has focal GCDFP positivity. The tumor cells have cytoplasmic and peripheral p63 staining (Figure 7). S-100 was also positive.
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Mammary analog secretory carcinoma (MASC) of the salivary gland is a newly recognized entity that resembles secretory carcinoma of the breast. These entities share a t(12;15)(p13;q25) translocation that results in an ETV6-NTRK3 fusion gene, which is the definitive means of diagnosis. In the past, MASC has been commonly classified as a zymogen poor acinic cell carcinoma or as an adenocarcinoma, not otherwise specified.
MASC is a rare, painless tumor that affects males more than females (1.4:1), while acinic cell carcinoma has a female predilection. The average age of diagnosis is 46 years. The parotid gland is the most frequently affected of the salivary glands but the entity has been seen in the soft palate, buccal mucosa, and base of tongue region. The tumor has a high rate of recurrence and has a higher rate of regional lymph node involvement than acinic cell carcinoma.
The gross tumor usually has a yellow to gray, rubbery, lobulated cut surface. The microscopic architecture may vary from solid to macrocystic or microcystic to papillary to tubular. Fibrous septa divide the mass. The malignant epithelial cells have mild cellular atypia with conspicuous vacuolization. The chromatin is finely granular, and central nucleoli are prominent. Mitoses are rare to absent. Serous acinar differentiation is absent, unlike in acinic cell carcinoma. The tumor may contain scattered plasma cells, and mild hemorrhage is common. Tumor necrosis is absent.
MASC tumors are strongly CK7, vimentin, mammoglobin, and S-100 positive. They are consistently GATA3 positive. The intraluminal secretions are PAS-positive and diastase-resistant. It is also positive for musicarmine, MUC1, and MUC4. Zymogen granules are absent. The tumor may have focal peripheral p63-positive staining pattern, which may represent an intraductal component and residual myoepithelial cells.
The ETV6-NTRK3 fusion gene has been linked to infantile fibrosarcoma, acute myeloid leukemia, and breast cancer. The gene product may activate the phosphatidylinositol 3-kinase pathway leading to transformation. It is proposed that the insulin-like growth factor (IFGR1) pathway may also have a role in tumor transformation. As ETV6 translocation testing becomes more readily available, the diagnosis of MASC may increase and, in turn, enable a more targeted chemotherapy option, such as tyrosine kinase or IFGR1 inhibitors.
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