TACSTD2 and Cowden syndrome 1: In conclusion, our results demonstrate that 1) Trop-2 is overexpressed in ~ 33% of CS, 2) primary CS cell lines overexpressing Trop-2 are highly susceptible to killing in vitro by SG, 3) SG in the presence of effector cells (NK cells) may induce significant ADCC against Trop-2 positive CS cells, 4) SG demonstrated a significant bystander killing effect, which could aid in treating tumors with heterogeneous antigen expression such as CS and 5) SG is highly effective in Trop-2+ CS xenografts.