As reported previously, two pairs of the regioisomeric mixtures of PPAPs had prominent anti-tumorigenic effect on human hepatocellular carcinoma through the inactivation of STAT3 [20]; we tested the anti-proliferative activity of these PPAPs in vitro using four human tumor cell lines (SGC7901, A549, HepG2, and MCF-7), as well as the antitumor mechanism of compounds 2 and 5 in MCF-7 cells. Here, STAT3 is linked to neoplasm.