Invasive Apocrine CA of Breast
Invasive apocrine carcinoma usually consists of small to medium sized nests with high-grade nuclei, although the example shown here has low-to-intermediate nuclear grade. There is abundant eosinophilic cytoplasm. The nests are surrounded by collagenous stroma. Many cases show chronic lymphocytic infiltrate.
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.