The tumor microenvironment consists of other cells besides cancer cells, including immune cells like T-cells, natural killer cells, and macrophages. The roles of these infiltrated cells, however, are diverse and can be both pro- or anti-tumorigenic. The effects of infiltrated natural killer cells are poorly characterized and highly misunderstood. To better study both the mechanics and effects of infiltrating NK cells, advances to 3D in vitro cancer models are necessary. To this end, I have developed a novel microfluidic device for culturing 3D tumor tissue, which can recapitulate the interstitial flow and gradient microenvironment. I utilize this device to create novel methods in quantifying NK cell infiltration and demonstrate the utility of this device for both infiltration and post-infiltration analysis.