An apparatus for capturing circulating tumor cells (CTCs) from blood. The apparatus includes a wearable device that receives fluid from vasculature of a subject through an input channel. A pump is coupled to the input channel the pump configured to receive blood at a first flow rate and to convert the flow of the blood to a second flow rate. The device further includes a replaceable candidate cell capture module having a microfluidic capture stage with herringbone channel structures configured to capture the candidate cells by antibodies. The device is further configured to provide the blood back to the vasculature of the subject.