Research to test whether improved chemopreventive efficacy could be achieved by combining submaximal doses of selective COX-2 inhibitors and selective retinoid for preventing HER-2 mammary tumorigenesis has shown that selective COX-2 inhibitor and retinoid in combination mediate greater-than-additive suppression of mammary tumor formation in HER-2 transgenic mice. Here, PTGS2 is linked to breast cancer.