Researchers have discovered that a low dose of the opioid antagonist naltrexone (LDN) markedly suppresses progression of human ovarian cancer transplanted into mice. LDN’s antitumor action was comparable to that of chemotherapy (cisplatin, taxol). LDN combined with cisplatin but not taxol had an additive inhibitory action on tumorigenesis. LDN offers a non-toxic and efficacious biologic pathway-related treatment that may benefit patients with this deadly cancer.