A microfluidic device for more accurately modeling the in vitro environment in which cancer occurs is disclosed. The device comprises a surface defining one or more microfluidic channels that may further comprise one or more endothelial cells, a first three dimensional scaffold comprising one or more cancer cells that is spatially separated from the one or more microfluidic channels, and a second three dimensional scaffold comprising one or more stromal cells, at least a portion of which is interposed between the one or more microfluidic channels and the first three dimensional scaffold. The second three dimensional scaffold is in fluid communication with both the first three dimensional scaffold and the one or more microfluidic channels. The device can be used to assay anti-cancer agents, or as a system for modeling the growth, behavior, or metastasis and tumor formation of cancer cells.