Mucinous cystadenocarcinoma of the breast with amplification of the HER2-gene confirmed by FISH: The first case reported

SummaryWe present the first case of a primary mucinous cystadenocarcinoma of the breast that, in addition to the characteristic immunophenotype (CK7+, CK20−, ER−, PR−, and cdx2−), showed a strong membranous HER2-protein expression and HER2-gene amplification documented by fluorescence in situ hybridization.