Modeling Early Metastatic Progression in Breast Cancer Using a Barrier‐Free, Perfusable Spheroid‐on‐a‐Chip Platform

Metastatic dissemination is the leading cause of cancer-related mortality, yet the early steps in this process remain difficult to study using current experimental models. Although organ-on-a-chip platforms recapitulate key features of the tumor microenvironment (TME), most fail to integrate physiologically relevant invasion, intravasation, and circulation within a single system. Membrane- and pillar-based designs hinder endothelial crossing and imaging, while open-interface approaches often lack stable perfusion and controlled positioning of 3D cell aggregates. Here, an open-port, barrier-free microfluidic device is presented, fabricated via surface treatment-based patterning, for investigating early metastatic progression from a tumor spheroid. The planar device incorporates a centrally confined gel matrix accessible via a top-loading port for precise spheroid placement, flanked by endothelialized lateral channels in direct contact with the matrix and perfusable under defined shear stress. Using MDA-MB-231 breast cancer spheroids, the model recapitulates key aspects of tumor cell migration, tumor-induced endothelial disruption, and intravasation, while enabling flow-mediated downstream recovery of viable intravasated cells. Overall, this device provides a physiologically relevant platform for the integrated, high-resolution, and longitudinal investigation of early metastatic events, providing a foundation for future mechanistic studies and molecular characterization of metastatic cell populations.