Immunohistochemical analyses of CD44 variant isoforms in invasive micropapillary carcinoma of the breast: comparison with a concurrent conventional invasive carcinoma of no special type component

Invasive micropapillary carcinoma (IMPC) is a distinct histopathological variant of breast carcinoma and frequently develops lymph node metastases. CD44 is a family of transmembrane glycoprotein receptors with multiple variant isoforms (CD44v), which have tissue-specific expression. Previous studies have demonstrated a loss or gain of CD44v and CD44 standard form (CD44s) expression in breast carcinomas. In this study, we analyzed the immunoprofiles of CD44s, CD44v6, and CD44v9 in IMPC and compared them with those in a concurrent invasive carcinoma of no special type (ICNST) component, thus clarifying the significance of CD44 expression in IMPC. Twenty-one consecutive cases of mixed IMPC were included in this study. The expression statuses of CD44s, CD44v6, and CD44v9 in both the IMPC and ICNST components were analyzed semiquantitatively by immunohistochemistry. The immunohistochemical scores of CD44s, CD44v6, and CD44v9 were significantly decreased in the IMPC component compared to the ICNST component (p = 0.00335 for CD44s, p = 0.000982 for CD44v6, and p = 0.00271 for CD44v9). Moreover, the immunohistochemical scores of CD44v6 in the IMPC component and CD44v9 in the ICNST component of lymph node metastasis cases were significantly lower compared to cases without lymph node metastasis (p < 0.01). Decreased CD44 expression may play an important role in promoting lymph node metastasis in IMPC through an inability or decreased capacity to bind with the surrounding stroma. Moreover, high CD44s(+) expression levels in the concurrent ICNST component may be related to the development of IMPC.