Apocrine morphology may be focally present in a variety of breast carcinomas, including ductal, lobular, mucinous, tubular, medullary and others. The term "apocrine carcinoma" is reserved for breast carcinomas in which majority of the tumor cells have apocrine morphology - consisting of abundant densely eosinophilic cytoplasm that may show granularity or vacuoles, enlarged nuclei and prominent nucleoli. They make up about 1% of all breast carcinomas. There are no major differences in the clinical features, mammographic presentation, or prognosis between apocrine and non-apocrine ductal carcinomas.Most cases of invasive apocrine carcinomas are negative for estrogen receptors (ER) and progesterone receptors (PR) and express androgen receptors (AR). About 50% of cases of pure apocrine carcinomas are HER2-negative. Gross cystic disease fluid protein 15 (GCDFP-15) - a marker of apocrine differentiation is expressed in majority of the cases, but it is not required to make the morphologic diagnosis of apocrine carcinoma.