Gene Expression In Breast Cancer

The Topic is Breast Cancer Gene expression using existing available data. These questions needs to be well explained: -The Gene Expression and its Role in breast cancer. -What is the point of gene expression analysis and why we use it in cancer? -In the report i need to know specifically about the Gene expression itself and what is in the gene expression data? -What are the Methods and how do scientists find out which gene expression causes the cancer based on their gene expression analysis and data. I am not really interested in cancer however, i really need specific information about gene expression and its role in breast cancer, please pay attention to the questions that were listed above. In reference i will need few articles about gene expression from scientific journals and textbooks.