Opiate Antagonists Can Inhibit Mammary Tumor Growth in Rats

Abstract
Female rats with carcinogen [7,12-dimethylbenz(a)anthracene] induced mammary adenocarcinomas were injected 2-3 times daily with naloxone or naltrexone, specific antagonists of endogenous opioid peptides. Both drugs completely prevented mammary tumor growth without inducing regression of the cancers, effects believed due to reduced prolactin and perhaps GH [growth hormone] secretion. A possible role is suggested for endogenous opioid peptides in rat mammary tumor growth.