2-Methoxyestradiol (2-MeOE2), an endogenous metabolite of 17β-estradiol (E2), is an inhibitor of microtubule assembly that inhibits the polymerization of tubulin and interferes with mitotic spindle dynamics leading to the blockage of mitosis of human cancer cells which lack estrogen receptors in metaphase. 2-MeOE2 is also an inhibitor of tumor growth and angiogenesis. Study results have shown that 2-MeOE2 induces mammalian cell transformation and genotoxicity in Syrian hamster embryo (SHE) fibroblasts through concentration-dependent inhibition of cell growth. Moreover, 2-MeOE2 has demonstrated anti-proliferative activity against estrogen-responsive breast cancer cell line MCF-7 and subsequent inhibition of the growth of tumors subcutaneously inoculated in mice.