This is a large scale experiment to find molecules that increase or decrease cancer growth. We measure each molecule’s activity by taking an image of cells grown in culture (here, cells taken from a desmoid tumor, a rare type of cancer). Based on how densely the cells are growing (here, visualized as a gradient from purple to yellow), we can assess the activity of each molecule. Such microscopy-based workflows enable these large scale screening experiments in many more cancers than other traditional methods.