Cancer survival would be transformed if it could be routinely detected at an early stage. This is currently not possible for most cancers due to the absence of markers with sufficient sensitivity and specificity. ctDNA is a new class of marker with exceptional specificity that has potential application to most cancer types. However, its sensitivity is currently modest for early stage disease due to the paucity of ctDNA molecules that can be purified from a standard 8ml blood draw. We propose to develop an indwelling device that will capture >36 fold more ctDNA over a 30 minute period, enabling this technology to routinely detect early stage cancer.