Reviewer(s): Dharam M. Ramnani, MD
Secretory carcinoma of the breast is a rare tumor that was initially described in children but the majority of cases have been reported in adults. It displays microcystic, solid, tubular/glandular, and pseudopapillary growth patterns. The tumor cells have abundant pale eosinophilic or amphophilic granular or vacuolated cytoplasm. The glandular/microcystic spaces contain PAS+ve diastase-resistant eosinophilic secretions. It is positive for alpha-lactalbumin, mammaglobin, lysozyme, S-100 protein and cytokeratins CK5/6 and CK8/18 with variable expression of CEA and GCDFP-15. They are usually negative for ER, PR, and HER2 and have a low Ki-67 labeling index. Secretory carcinoma of breast may be related to acinic cell carcinoma of salivary glands. A similar molecular genetic abnormality has been found in both tumors - a recurrent balanced chromosomal translocation, t(12;15)(p13;q25), which leads to the formation of ETV6-NTRK3 fusion gene. It is a relatively indolent tumor with an excellent overall prognosis.