Finally, despite C39 tumors having approximately 6.5-fold more Trop-2 expression than C13 tumors, there was no significant difference in antitumor effects between the two when treated with SG, suggesting that once a certain threshold of SN-38 delivery to the tumor is reached, maximum DNA damage is inflicted on the cells, and addition of more SN-38 above this will not enhance the effects. This evidence concerns the gene TACSTD2 and neoplasm.