Mammaglobin and S-100 immunoreactivity in salivary gland carcinomas other than mammary analogue secretory carcinoma.

Mammary analogue secretory carcinoma (MASC) is a recently described salivary gland tumor that has morphologic features similar to secretory carcinoma of the breast and that also harbors the same ETV6 translocation. Diffuse mammaglobin and S-100 immunoreactivity are used to differentiate MASC from its morphologic mimics, especially acinic cell carcinoma and adenocarcinoma, not otherwise specified. However, the combination of mammaglobin and S-100 immunoreactivity has not been well studied in other types of salivary gland carcinomas that may have focal areas reminiscent of MASC. Here we evaluated mammaglobin and S-100 immunoreactivity in 15 cases each of polymorphous low-grade adenocarcinoma, adenoid cystic carcinoma and mucoepidermoid carcinoma, and also in 2 cases of adenocarcinoma, not otherwise specified, and 1 mucinous adenocarcinoma. Cases with significant co-expression of mammaglobin and S-100 (moderate or strong immunoreactivity in >25% of tumor cells) were further analyzed by fluorescence in situ hybridization using the ETV6 (12p13) break-apart probe. Nine cases (60%) of polymorphous low-grade adenocarcinoma and two (13.3%) of adenoid cystic carcinoma met the criteria for significant co-expression of mammaglobin and S-100. All were negative for the ETV6 translocation by fluorescence in situ hybridization. Although mammaglobin and S-100 positivity was seen in the majority of polymorphous low-grade adenocarcinomas and a minority of adenoid cystic carcinomas, none were positive for the ETV6 translocation characteristic of MASC. This indicates a need for caution in the use of immunohistochemistry for diagnosing MASC, especially in the absence of cytogenetic confirmation.