Secretory
breast carcinomas (<0.15% of
breast tumors) are associated with a characteristic morphology and a favorable prognosis. Remarkably, this entity is the only epithelial
tumor of the breast with a balanced translocation, t(12;15), that creates an ETV6-NTRK3 gene fusion encoding chimeric
tyrosine kinase also encountered in cellular
mesoblastic nephroma and infantile
fibrosarcoma. The aim of this study was to determine the phenotypic class (ie
luminal A/B, ERBB2, basal-like) of
secretory breast carcinoma. A series of six secretory
breast carcinomas were identified in our files. The ETV6 rearrangement was confirmed in all cases by fluorescence in situ hybridization. Immunophenotype was assessed with anti-ER, PR, ERBB2, KIT, EGFR,
E-cadherin,
vimentin, PS100, smooth muscle actin, basal (CK5/6 and 14),
luminal cytokeratins (CK8/18) and p63
antibodies. In situ and invasive components shared the same immunoprofile and were ER, PR, ERBB2 negative with expression of basal cytokeratins. ETV6 gene alterations were present in both in situ and invasive components, highlighting their genetic similarities. The immunoprofile data (triple-negative with expression of basal markers) showed that secretory
breast carcinomas with ETV6-NTRK3 fusion gene belong to the phenotypic basal-like spectrum of
breast carcinomas. These results support the hypothesis that secretory
breast carcinomas have immunohistochemical and genetic features that distinguish them from other basal-like
tumors of the breast.