Blood has been widely used as a minimal invasive biopsy for disease diagnosis. Enumeration of the rare circulating tumor cells (CTC) is currently a FDA-approved method for prognosis evaluation in metastatic breast, colorectal and prostate cancer. To study the rare CTC, we propose to enumerate CTCs and generate a true, unbiased, total RNA transcriptome from single-CTCs with microfluidic devices. The study will facilitate a large scale CTC molecular characterization for treatment evaluation in breast cancer patients.