ERBB2 and breast cancer: To compare drug responses between the different 3D cell culture conditions, JIMT1 breast cancer cells were screened with two different drug libraries: a MicroSource cancer compound library with 80 compounds in four dilutions, each in one replicate, and a custom 22 compound library mainly consisting of HER2+ cancer-targeted drugs in seven dilutions, each in two intra-plate replicates (File S1).