SP4 and colonic neoplasm: These results, coupled with in vivo data showing that the sodium salt of aspirin decreased colon tumor growth in a xenograft model (RKO cells) in athymic nude mice and also decreased levels of Sp1, Sp3 and Sp4 proteins in tumors (Fig. 7), suggest that aspirin-induced downregulation of Sp proteins plays a role in the anticancer activity of this compound.