We analyzed immunohistochemically the expression of CD24 and spliced variants of CD44v5 and v9 in invasive micropapillary carcinoma (IMPC) of the breast that is a rather aggressive tumor characterized by alteration of cells adhesion molecules, early lymph node metastases and poor prognosis. We analyzed 31 high-grade IMPCs and compared their expression to 22 high grade (G3) invasive ductal carcinomas of the breast (IDCs). We found a higher expression of CD24 in high-grade IMPCs with a peculiar inverted apical localization, compared to IDCs, showing a strong cytoplasmic staining; normal breast tissue resulted completely negative. IMPCs showed reduced expression of CD44v5 and CD44v9 compared with IDCs, but without a statistical significant difference. This study demonstrated that IMPC represents a distinct entity of breast carcinoma with high expression of CD24 with a typical inverted apical membrane pattern and reduction of CD44 isoforms v5 and v9, compared to IDCs. These features could explain the high lymph-vascular invasion propensity and higher metastatic capability of these tumors and could be a useful tool for a future targeted therapy.
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