Abstract
Mammary analogue secretory carcinoma (MASC) is a recently described entity in the differential diagnosis of salivary gland tumors. It is notable for a characteristic t(12;15)(p13;q25) translocation that results in a unique fusion protein, ETV6-NTRK3 . While several studies have retrospectively identified this translocation in cases previously diagnosed as a different salivary malignancy, there have been relatively few cases where this translocation was identified on initial pathology results, and fewer still in a pediatric population. We present a case of a 15 year old female with a slowly enlarging, painless, left facial mass. MRI demonstrated a cystic mass extending into the deep lobe of the parotid, and she underwent parotidectomy. The tumor cells stained positive for S100 and CK19. ETV6 translocation was present, confirming the diagnosis. Mammary analogue secretory carcinoma is a recently described tumor of the salivary glands, which often masquerades as more common primary salivary gland tumors and cysts. More research is needed to characterize the typical behavior of this neoplasm and the optimal treatment regimen. With identification of its characteristic translocation, mammary analogue secretory carcinoma can be easily differentiated from its more prevalent counterparts, and should therefore remain within the differential of the pathologist and head and neck surgeon.
1
Introduction
Mammary analogue secretory carcinoma (MASC) is a recently described tumor that displays histologic features of more common salivary gland neoplasms, such as tumor cells with central nuclei and pale pink granulated or vacuolated cytoplasm. Because of this, it has historically mimicked adenocarcinoma and acinic cell carcinoma, among others . Since the original published series of 16 cases, multiple studies have retrospectively shown tumors classified as these more common entities to in fact be MASC with ETV6 translocation on FISH. Even so, very few cases of MASC have been reported in the literature and even fewer in children.
2
Case report
A 15 year old female presented with a slowly enlarging left facial mass following a non-diagnostic fine-needle biopsy and cyst aspiration procedure. The mass had been present for several months but the facial nerve was functional at the time of presentation. Her history was otherwise unremarkable. Physical exam revealed a firm, fixed, 3 cm mass within the left parotid gland. MRI demonstrated a well-circumscribed 2.9 × 2.6 × 3.0 lesion within the deep lobe without evidence of osseous invasion ( Figs. 1–3 ). There were internal T2 hyper-intensity and intermediate T1 signal with a dependent fluid level noted. She underwent a superficial parotidectomy with facial nerve dissection. A large, well circumscribed, cystic mass was identified and removed with a cuff of parotid tissue. The specimen demonstrated a dominant cyst with intracystic fragments of solid and papillary tan tissue with surrounding atrophic salivary gland tissue. Microscopically, within the lumen of the cyst were focal areas of neoplastic epithelial proliferation composed of uniform polygonal epithelial cells, some forming duct structures filled with bright eosinophilic seromucinous material and some forming papillary structures. The tumor cells stained positive for S100 and CK19 by immunohistochemistry. Subsequent fluorescence in situ hybridization (FISH) confirmed a rearrangement of the ETV6 gene and the diagnosis of MASC was established. The patient was discussed with head and neck tumor board members and the decision was made not to pursue post-operative radiation therapy or completion parotidectomy. An adjacent parotid lymph node on postoperative baseline imaging was found to be negative on subsequent fine needle aspirate.
