Device and method for comminution or inactivation of circulating tumor cells (CTC) or tumor cell clusters (CTCC) from a tumor-affected organ or organ part, wherein it is proposed that in the venous drain of the tumor-affected organ or organ part a pump (2) with a pressure-increasing section and a pressure-reducing throttle (13) is arranged and is operated at the output side in its design point given by volumetric flow (Q) and pumping pressure (p) according to the volumetric flow and the blood pressure of the venous drain of the tumor-affected organ or organ part. Circulating tumor cells (CTC) and tumor cell clusters (CTCC) are thus comminuted and inactivated to thus reduce the risk of metastasis formation in cancerous diseases.