Besides tumor cells, the microenvironment harbors a variety of host-derived cells. To date, the most successful tissue engineering approaches have employed methods that recapitulate the composition, architecture and/or chemical presentation of the native microenvironment. Thus tumor engineering in biomimetic three dimensional conditions represents a dynamic cooperatively between different cell types in a spatially and functionally accurate fashion. Evidence has been provided that the cross-talk between tumor cells and stromal cells leads to enhanced tumor growth, metastasis and altered response to chemotherapeutic agents. It has been provided that endothelial cells play an important role in tumor in shaping the tumor microenvironment and controlling tumor development, in particular through neo-angiogenesis. We developed a 3D in vitro tumor model that encompasses a cross-linked hyaluronic acid hydrogel providing a physiologically relevant microenvironment for mammary tumor cell and endothelial cell co-culture. We investigated the morphological cross-talk between tumor and endothelial cells in a 3D configuration. Additionally, we observed the influence of co-culturing on the proliferation, angiogenic protein expression and secretion. We demonstrated that endothelial cells tend to acquire a spheroidal configuration with the mammary tumor cells surrounding the endothelial spheroid. We also observed that the levels of VEGF, MMP-2 and MMP-9 have tendencies to decrease within the first 6 days of co-culture, and tend to increase at day 12. This could be due to the restored polarity of the mammary tumor cells leading to a period of quiescence required to restore the malignant organization. These data confirm the importance of tissue architecture and polarity in malignant progression.