The isolation and rapid molecular characterization of circulating tumor cells (CTCs) from a liquid biopsy could enable the convenient and effective characterization of the state and aggressiveness of cancerous tumors. Existing technologies enumerate CTCs using immunostaining; however, these approaches are slow, labor-intensive, and often fail to enable further genetic characterization of CTCs. Here, we report on an integrated circuit that combines the capture of CTCs with the profiling of their gene expression signatures. Specifically, we use a velocity valley chip to efficiently capture magnetic nanoparticle-bound CTCs, which are then directly analyzed for their gene expression profiles using nanostructured microelectrode biosensors. CTCs are captured with 97% efficiency from 2 mL of whole blood, yielding a 500-fold concentration within 1 h. We show efficient capture of as few as 2 cancer cells/(mL of blood) and demonstrate that the gene expression module accurately profiles the expression of prostate-specific genes in CTCs captured from whole blood. This advance provides the first sample-to-answer solution for gene-based testing of CTCs. The approach was successfully validated using samples collected from prostate cancer patients: both CTCs and prostate-specific antigen (PSA) mRNA sequences were detected in all cancer patient samples and not in the healthy controls.