A microfluidic device for more accurately modeling the in vitro environment in which cancer occurs is disclosed. The microfluidic device includes a surface defining one or more microfluidic channels, a first three dimensional scaffold comprising one or more cancer cells that is spatially separated from the one or more microfluidic channels, a second three dimensional scaffold, at least a portion of which is contacting and in fluid communication with the first three dimensional scaffold, and that is spatially separated from the one or more microfluidic channels, and a third three dimensional scaffold, at least a portion of which is contacting and in fluid communication with the one or more microfluidic channels and the second three dimensional scaffold. 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.