Isoforretin A (IsoA) is a novel ent-kaurane constituent isolated from a traditional Chinese medicinal herb of the Isodon genus and has multiple anticancer effects both in vitro and in vivo. IsoA inhibits Trx1 activity by covalently binding to the Cys32/Cys35 residues in the Trx1 activation site, resulting in ROS accumulation and causing DNA damage and apoptosis in tumor cells. The gene discussed is TXN; the disease is neoplasm.