Carcinoma of breast with apocrine differentiation: A distinct entity with typical histomorphology and molecular signature

Abstract

Apocrine Carcinoma (APC) is a rare and distinct entity among all the histological variants of invasive ductal carcinoma(IDC) of breast. It is common to encounter focal apocrine differentiation, but only 4% of IDCs show extensive apocrine differentiation. In the 2012 WHO classification of tumors of breast, it is placed under specialized subtypes of IDC and named “carcinomas with apocrine differentiation.” Apocrine differentiation is seen with IDC-no specific type (IDC-NST) as well as in special type carcinomas such as tubular, lobular, micropapillary, and medullary and that's why it does not represent as a separate entity. Although clinical, radiological, and gross appearance is indistinguishable from IDC-NST (the most common form), APC has a typical histomorphological picture with distinct molecular apocrine signature and immunohistochemistry. It is characterized by increased androgen expression overlapping with HER2/neu expression and estrogen receptor (ER) as well as progesterone receptor (PR) negativity. It is thought to have worse prognosis; hence, diagnosing this entity at the earliest is very important for implementation of new treatment modalities. Here, we report two such cases of carcinomas with apocrine features – 47-year-old and 52-year-old patients showing features of apocrine carcinoma and positivity for androgen receptor with negativity for ER and PR.