Immunohistochemical expression of mammaglobin in salivary duct carcinomas de novo and salivary duct carcinoma ex pleomorphic adenoma

Mammaglobin is expressed in breast and salivary gland secretory carcinomas; however, its expression in salivary duct carcinomas (SDCs) still not well established. Therefore, the aim of this study was to investigate the presence and distribution of mammaglobin immunoexpression in SDC ex-PA in different phases of the adenoma to carcinoma sequence evaluating its possible involvement in carcinogenesis and tumor progression, as well as to determine its expression in SDC de novo. Mammaglobin immunohistochemistry was performed in 84 SG tumors, including 41 pleomorphic adenomas (PA) without malignant transformation, 13 intracapsular SDC ex-PA, 5 frankly invasive SDC ex-PA, 25 SDC de novo and 10 secretory carcinomas. The reactions were qualitatively analyzed and digitally scored. Positive immunostaining for mammaglobin was observed in 37 out of 84 SG tumors evaluated (44.1%), but strong staining was consistently seen only in secretory carcinomas, SDC de novo and frankly invasive SDC ex-PA, while it was weaker in intracapsular SDC ex-PA and PA. In PA, mammaglobin expression was significantly associated with recurrence. This study has confirmed that the mammaglobin is commonly expressed in SDC de novo and secretory carcinomas. Its expression was higher in SDC ex-PA than in PA, suggesting that mammaglobin may play a role in its malignant transformation.