BACKGROUNDMammary analogue secretory carcinoma (MASC) with an ETS variant gene 6 (ETV6)–neurotrophic tyrosine kinase receptor type 3 (NTRK3) translocation is a newly described type of salivary gland cancer. It is known that overexpression of signal transducer and activator of transcription 5a (STAT5a) occurs in secretory carcinoma of the breast and MASC, and STAT5a expression may be related to the ETV6‐NTRK3 translocation. It was hypothesized that phosphorylated signal transducer and activator of transcription 5 (p‐STAT5) might be specifically expressed in MASC of the salivary gland.METHODSThe expression of p‐STAT5 and mammaglobin (MMG) was examined with immunohistochemistry (IHC)/immunocytochemistry (ICC) in tissue sections from 58 salivary gland cancers (8 MASCs and 50 other salivary gland cancers) and in cytological smears from 17 salivary gland cancers (7 MASCs with paired histologic samples and 10 other salivary gland cancers).RESULTSp‐STAT5 IHC was clearly increased in MASC versus normal salivary gland tissue and other salivary gland cancers. p‐STAT5 expression was found in 7 of 8 MASCs (87.5%) and in none of the 50 other salivary gland cancers (0%) by IHC. On cytology, p‐STAT5 expression was found in all cases of MASC (7 of 7 or 100%) but in none of the 10 other salivary gland cancers (0%) by ICC. The expression rate of MMG by histology and cytology was higher than that of p‐STAT5 in the other salivary gland cancers.CONCLUSIONSp‐STAT5 might be useful as a detection marker of MASC in the differential diagnosis of salivary gland cancers, and initial screening with p‐STAT5 IHC/ICC, combined with auxiliary fluorescence in situ hybridization confirmation, is a reliable, economical approach to identifying MASC of the salivary gland. Cancer (Cancer Cytopathol) 2015;123:603–11. © 2015 American Cancer Society.