Hemorrhage of MRI and Immunohistochemical Panels Distinguish Secretory Carcinoma From Acinic Cell Carcinoma

OBJECTIVES: Secretory carcinoma (SC, mammary analogue secretory carcinoma) is a salivary gland tumor with ETV6‐NTRK3 gene fusion, and its differential diagnosis includes acinic cell carcinoma (ACC). As hemorrhage is often seen in SC, we hypothesized that magnetic resonance imaging (MRI) and immunohistochemical analyses could distinguish SC from ACC. STUDY DESIGN: Retrospective study. METHODS: We used ETV6‐NTRK3 gene fusion analyses to reclassify 19 parotid gland tumors that had previously been diagnosed as SC or ACC, and then investigated hemorrhage in both hematoxylin‐eosin (H&E)‐stained sections and MRIs, and immunohistochemical expression of S‐100, mammaglobin, DOG1, and α‐amylase. RESULTS: The 19 tumors were genetically reclassified into 11 (58%) SC and 8 (42%) ACC. Combined S‐100 and mammaglobin were specific for SC; whereas DOG1 was specific for ACC, and α‐amylase was expressed only in 4 ACC cases (50%). H&E staining showed hemorrhage with hemosiderin deposition in all SC cases, and T2‐weighted MRI showed hypointense areas in all investigated SC cases, but not in ACC. CONCLUSION: Hemorrhage with hemosiderin deposition is frequently present in SC, and hemorrhage findings in MRI and an immunohistochemical panels for S‐100, mammaglobin and DOG1 can distinguish SC from ACC. LEVEL OF EVIDENCE: 3b