Mammaglobin and GCDFP are commonly used as IHC markers of mammary origin. Mammaglobin is more sensitive than GCDFP, but both label the majority of ER+ breast carcinomas as well as HER-2+ breast carcinomas. However, mammaglobin and GCDFP have markedly lower sensitivity for triple negative breast carcinoma with limited diagnostic utility Both immunostains are cytoplasmic and often show variable or focal labeling across a carcinoma. GCDFP is more specific for breast carcinoma than mammaglobin. The main differential diagnosis to consider in a carcinoma that labels for GCDFP and mammaglobin is adnexal carcinoma such as apocrine carcinoma; however, this distinction can usually be resolved by identifying an associated carcinoma in situ or by reviewing the clinical presentation of whether the mass is centered in the breast or dermis.