Tumor endothelial interaction, CD44+/CD24- stem cell signature, and prognosis in early-stage breast cancer

Abstract

503 Background: The effects of tumor-endothelial interaction on global gene expression in breast cancer are not yet well characterized. We hypothesized that gene expression signatures induced by tumor-endothelial interaction might be of clinical relevance. Methods: To this aim we set up an ex vivo co-culture model with human benign and a panel of 6 malignant breast epithelial cells in combination with human venous and microvascular endothelial cells and determined associated gene expression changes with cDNA microarrays. Pretreatment gene expression profiles of 295 early stage breast cancers from the Netherlands Cancer Institute with a median follow up of 12.6 years allowed evaluating in vitro effects in vivo. Results: The most prominent response to co-culture was the induction of a set of “M-phase cell cycle” genes in a subset of breast cancer co-cultures, which were absent in co-cultures with normal breast epithelial cells. While in monoculture tumor cells containing the stem cell like CD44+/CD24- signature showed a lower expression of the “M-phase cell cycle” genes than the CD44-/CD24+ cells, in the co-cultures with CD44+/CD24- cells these genes were induced. Interestingly, these tumor cells co- expressed a set of angiogenic factors such as VEGF, PTN, and FGF12 mRNA at significantly higher levels. In vivo, the expression of the gene set derived from the co-culture was remarkably coherent providing a basis for segregation of tumors into two groups. In a univariate analysis, early stage tumors with high expression levels (n= 137) of “M-phase cell cycle” genes had a significantly lower distant metastasis-free survival (p=1.8e-5) (50 % at 10 years) and overall survival rate (p= 5e-9) (52 % at 10 years) than tumors with low expression levels (n= 158) (metastasis-free survival: 73 %; overall survival: 84 % at 10 years). Conclusions: Our results suggest that the interaction of tumor cells expressing the CD44+/CD24- stem cell like signature, implicating a low proliferative potential, with endothelial cells might explain the unexpected and paradoxical association of the CD44+/CD24- signature with highly proliferative tumors with an unfavorable prognosis. Multiple co-expressed angiogenic factors represent potentially interesting additional therapeutic targets. No significant financial relationships to disclose.