Many tumors exist in vivo as three-dimensional masses. In order to better model the dynamics of three-dimensional tumor growth and immune cell invasion, cancer cell lines are grown in low-adhesion plates that force them to interact with each other, forming a spheroid. After spheroids form in culture, immune effectors and drugs are added to the wells and their effect on the tumor mass is measured by transmitted light or fluorescence microscopy in a live-cell image system (IncuCyte, Sartorius Inc).