TACSTD2 and neoplasm: To evaluate the ability of SG to induce a bystander killing effect in a tumor environment where Trop-2 is expressed heterogeneously we tested the ADC activity by admixing SARARK9 (ie, high Trop-2 expression) in vitro with low/negligible Trop-2 expressing cells (i.e., GFP-ARK4 cells) for 72 hrs (cells were incubated with the drugs for 12 hrs as stated in the materials and methods section).