The sieving and enrichment of rare tumor cells from large-volume pleural effusion(PE)samples is a promising technique for cell-based lung tumor diagnosis and drug tests,which features high throughput and recovery,purification,as well as viability rates of rare target cells as the prerequisites for high sensitivity,specificity,and accuracy of tumor cell analysis.In this paper,we propose a three-dimensional(3D)sieving method for rare tumor cell enrichment,which effectively eliminates the“dead zones”in traditional two-dimensional(2D)cell filters with a dimension-raising strategy to satisfy the requirements mentioned above.The prototype device was combined with a funnel-shaped holder,a flexible micropore membrane in the middle,and a 3D spiral fluid channel covered on the membrane as a three-layer ice-creaming cone composite structure.Driven by gravity alone,the device performed as follows:(1)20-fold throughput compared with the 2D commercial plane cell filter,which was up to 20 mL/min for a threefold dilution of whole blood sample;(2)high recovery rates of 84.5％士21％,86％±25％,83％士 14％for 100,1000,and 10 000 cells/mL,respectively,in 30 mL phosphate buffer saline(PBS)sample,and a 100％positive detection rate in the case of≤5 A549 cells in 1 mL PBS;(3)a typical purification rate of 85.5％±9.1％;and(4)a viability rate of＞93％.In the demonstration application,this device effectively enriched rare target cells from large volumes(＞25 mL)of clinical pleural effusions.The following results indicated that tumor cells were easy-to-discover in the enriched PE samples,and the proliferation capability of purified cells was(＞4.6 times)significantly stronger than that of unprocessed cells in the subsequent 6-day culture.The above evaluation indicates that the proposed easily reproducible method for the effective execution of rare cell enrichments and assays is expected to become a practical technique for clinical cell-based tumor diagnosis.