Embodiments in accordance with the present invention relate to methods and apparatuses for concentrating and isolating Circulating Tumor Cells (CTCs) from body fluids. One embodiment of the present invention includes a micro-fabricated or nano-fabricated device having channels configured for separating and excluding. Embodiments in accordance with the present invention utilize features that reduce the hydrodynamic pressure experienced by the cells during the separation, isolation and concentration processes, and therefore reduce the likelihood of cell lysis or other damage to the cells.