Most Non-Parotid “Acinic Cell Carcinomas” Represent Mammary Analogue Secretory Carcinomas
Justin A Bishop, Raluca Yonescu, Denise Batista, William H Westra. Johns Hopkins Hospital, Baltimore, MD
Background: Acinic cell carcinoma (ACC) is a low grade salivary gland malignancy characterized by serous acinar differentiation. Most ACCs arise in the parotid gland, but ACCs in non-parotid sites, where serous acini are less abundant, have been reported. Given the recent discovery of mammary analogue secretory carcinoma (MASC) – a salivary malignancy defined by ETV6-NTRK3 gene fusion that histologically mimics ACC – a retrospective re-evaluation of non-parotid ACCs is warranted.
Design: The surgical pathology archives of The Johns Hopkins Hospital were searched for all ACCs arising outside of the parotid gland. For each case, the histologic slides were closely reviewed and immunohistochemistry (mammaglobin, S100 protein) was performed. A confirmatory ETV6 break-apart FISH assay was attempted on each tumor. Demographic and clinical outcomes data were extracted from patient medical records.
Results: Fourteen carcinomas from non-parotid sites (11 oral, 2 submandibular, 1 sinonasal) diagnosed as ACC were identified. ETV6 FISH analysis showed that 11 of 14 (79%) cases, including 9 of 11 (82%) oral cavity tumors and 2 of 2 (100%) submandibular tumors, were actually MASCs. The MASCs exhibited uniform eosinophilic cells with vacuolated cytoplasm, microcystic and papillary architecture, intraluminal secretions, and frequent cyst formation. All three FISH-negative carcinomas exhibited overt serous acinar differentiation in the form of basophilic cytoplasmic granules. Immunohistochemistry for mammaglobin and S100 was strongly positive in all 11 MASCs, but negative in the 3 true ACCs. The MASCs occurred in 7 women and 4 men ranging from 20-86 years (mean, 56 years), and usually presented as painless masses. Follow up information was available for 10 of 11 MASCs; only one tumor locally recurred, and no tumors metastasized.
Conclusions: While ACC does rarely arise outside the parotid gland, most non-parotid salivary gland carcinomas with features of ACC are actually MASCs. As a result, the diagnosis of ACC outside the parotid gland should be reserved for cases that exhibit basophilic cytoplasmic granules. Immunohistochemical stains for mammaglobin and S100 are helpful adjunctive tests, and ETV6 FISH is confirmatory. Like ACCs, extra-parotid MASCs appear to be low grade with limited capacity for aggressive clinical behavior, thus diminishing the impact of tumor misclassification.
Category: Head & Neck
Monday, March 4, 2013 1:00 PM
Proffered Papers: Section F, Monday Afternoon