Secretory breast carcinoma: unique, triple-negative carcinoma with a favorable prognosis and characteristic molecular expression.

Secretory carcinoma is a rare but distinct subtype of breast carcinoma, with characteristic histomorphology and generally favorable prognosis. Although it was originally described as a juvenile breast carcinoma, occurring in young children, most cases have been reported in adults of both sexes. As the name implies, the characteristic histomorphology is the presence of a large amount of intracellular and extracellular, eosinophilic secretion material that stains positive for periodic acid-Schiff. Most tumors stain positive for S100 and negative for estrogen receptor, progesterone receptor, and ERBB2 (formerly HER2/neu) (ie, triple negative). In addition, some secretory carcinomas demonstrate a basal-like immunoprofile. Recent studies have shown the characteristic molecular feature: a balanced translocation t(12;15), resulting in an ETS variant 6-neurotrophic tyrosine kinase receptor type 3 (ETV6-NTRK3) fusion gene encoding a chimeric tyrosine kinase. Although rare events of axillary lymph node or distant metastases have been documented, the prognosis is generally excellent. The methods of surgical treatment and the role of adjuvant therapy, particularly for young patients, remain controversial.