cDNA expression profiling reveals elevated gene expression in cell clusters overlying focally disrupted myoepithelial cell layers: implications for breast tumor invasion.

BACKGROUND: Our previous studies revealed that a subset of mammary ductal carcinoma in situ (DCIS) contained focally disrupted myoepithelial (ME) cell layers that were predominantly overlain by estrogen receptor (ER) negative cells, which showed a substantially higher rate of cell proliferation and genetic alterations than adjacent ER positive cells within the same duct. This study attempted to assess whether these cells also had a different expression profile on tumor progression related genes.
DESIGN: Consecutive sections were made from frozen tissues of 30 DCIS with focally disrupted ME cell layers and associated ER negative cell clusters. ER negative and adjacent ER positive cells within the same duct were microdissected for RNA extraction and amplification. Amplified RNA was converted to biotin-labeled cDNAs and interrogated with 'Cancer PathwayFinder' arrays.
RESULTS: Cells within each or among ER negative clusters were immunohistochemically and morphologically similar, whereas they differed substantially from adjacent cells within the same duct. Of 20-paired informative ER negative and positive cells, 15 genes were differentially expressed. Of which, 11(73.3%) were higher in ER negative, 2 (13.3%) were higher in ER positive, and 2 (13.3%) were equal in these cells (p <0.01). Of 11 up-regulated genes in ER negative cells, 8 indirectly or directly promote proliferation and progression, and 3 promote apoptosis.
CONCLUSION: ER negative cell clusters showed a significantly higher expressing frequency of multiple tumor progression related genes than their adjacent ER positive counterparts, suggesting that they are likely to be biologically more aggressive and have a greater potential for invasion.