High Level CD24 Expression Is Correlated to Higher Metastatic Potential of Breast Cancer Cells.

Cancer stem cells are subpopulations of cancer cells with potential to seed and develop new cancer mass causing recurrence and/or metastasis, but phenotypic characteristics of such cell populations remains uncertain. As an initial approach to identify heterogeneity in cancer mass, we performed comparative study using matched pairs of primary breast cancer masses and their immediate metastatic counterparts in regional LN.

First, in the gene expression study of primary tumor mass and their LN counterpart using cDNA microarray, about 100 genes showed differential expression between the two, but with variations depending on cases (3 Exp). In addition, when fresh individually matched surgical block from primary mass and LN mass were each inoculated into NOD/SCID mice, higher growth of LN-derived mass was observed supporting distinction between the two (2 Exp). In subsequent search for phenotypic difference between the two, 99 primary-LN tissue pairs with individual matching were immunostained for CD24, a newly proposed marker for cancer stem cell, and analysed by semiquantitative scoring (0, 1+, 2+, 3+, 4+). Among 73 cases with positive staining for CD24, higher level of CD24 expression in LN mass compared to its matched primary tumor tissue was observed in 38 cases (52.1%), while the opposite was for only 7 cases (9.6%). Furthermore, high level expression (4+) of CD24 was observed more frequently in LN tumor tissues (63.0%, 46/73) than in their primary tumor counterparts (26%, 19/73)( P = 0.000). These results support the notion that cancer cells in tumor mass are clonally heterogeneous and suggest that CD24 expression could be related to characteristic of metastatic cancer stem cells.