This directional migration of endothelial cells to assume tumorangiogenesis should be attributed to the VEGF secretion bythe MCF-7 spheroid, which showed a similar trend with thespheroids cultured alone (Figure 6F). Meanwhile, the outwardinvasion of the MCF-7 cells from the spheroid was also pre-sent during the period of culture, similar to when the sphe-roids were embedded in the matrices alone (Figure 6E).