Colon cancer patients on low dose aspirin therapy (75 mg/d; ca. 1 mg/kg/d) would exhibit maximum average serum concentrations of salicylate (6.8 mM) and aspirin (0.21 mM) sufficient to inhibit colon cancer cell growth and decrease expression of Sp1, Sp3, Sp4 and Sp-regulated genes (Fig. 3). This evidence concerns the gene SP4 and colonic neoplasm.