Fenbendazole (methyl N-(6-phenylsulfanyl-1H-benzimidazol-2-yl) carbamate) is a broad spectrum benzimidazole anthelmintic used for treatment of gastrointestinal parasites in dogs, cats, ferrets, rabbits, sheep, cattle, fish and reptiles. It has been found to be effective against worms such as giardia, roundworms, hookworms, whipworms, the tapeworm genus Taenia (except Dipylidium caninum, common dog tapeworm), flukes, lungworms and pinworms in humans and dogs and against most intestinal trematodes in pigs. It also has been used to control a number of pulmonary nematodes in cats, and has shown limited activity against some flukes, lungworms and a variety of helminth intestinal parasites in horses. Several studies in tumor models have demonstrated that fenbendazole has antitumor activity and interferes with cellular mitosis and glucose metabolism. These results have prompted preclinical and clinical investigations of the potential roles of benzimidazoles in cancer. To evaluate the anticancer effects of fenbendazole, we performed an experiment in which mice bearing EMT6 tumors were treated with praziquantel and/or fenbendazole as described above. At the time of randomization, the tumor volume of each mouse was determined and then compared with four-times that volume at the time of treatment to determine the growth rate. We found that fenbendazole, either alone or in combination with praziquantel or cisplatin, did not significantly alter tumor growth in unirradiated mice, but that fenbendazole did reduce the rate of growth in irradiated mice. These data, taken together, do not support the use of fenbendazole in facility treatment programs to eradicate pinworms in research mice. However, the research veterinary community must recognize that facility-wide fenbendazole treatments may have unintended immunosuppressive effects and therefore must be cautious when using these drugs in the presence of experimental animals with compromised immune systems. fenbendazole capsules
