Breast cancer cells with a CD44(+)/CD24(-/low) phenotype have been suggested to have tumor-initiating properties. It is unclear whether their presence correlates with clinicopathological features of invasive micropapillary carcinoma (IMPC) of the breast, an unusual subtype of breast cancer with a high incidence of lymph node metastasis and poor prognosis. CD44 and CD24 expression was determined by double-staining immunohistochemistry in 103 cases of IMPC and in 94 cases of invasive ductal carcinoma (IDC). The prevalence of CD44(+)/CD24(-/low) tumor cells was higher in IMPC than in invasive ductal carcinoma IDC (P=0.018). The CD44(+)/CD24(-/low) tumor cells were also detected in adjacent stroma surrounding the micropapillary structure in 53.4% (55/103) of IMPC, but only in 7.4% (7/94) of stroma of IDC. These tumor cells in stroma of IMPC were positive for vimentin and α-smooth muscle actin, and negative for E-cadherin. The CD44(+)/CD24(-/low) tumor cells in the micropapillary structure of IMPC were associated with those in stroma (P=0.000). Moreover, they were both associated with lymphovascular invasion and extranodal extension, respectively (P<0.05). The proportion of CD24(+) tumor cells was also higher in IMPC than in IDC (P=0.035), and the CD24(+) tumor cells were associated with lymph node metastasis in IMPC (P=0.010). The results suggest that the increased proportion of CD44(+)/CD24(-/low) tumor cells and CD24(+) tumor cells and the epithelial mesenchymal transition may play an important role in aggressiveness and high metastatic risk of breast IMPC.
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