An 80-year-old woman with metastatic melanoma presented to our clinic in late July 2019 with a recent rise in CEA levels and hepatocellular injury. Her physical findings and vital signs were unremarkable, but her family reported that she had begun taking oral fenbendazole—a marketed anthelmintic for dogs—since early April based on information on social media sites purporting to be effective against cancer.
She had been receiving pembrolizumab monotherapy as her first line of treatment. The patient was asymptomatic and had been doing well on the therapy until her recent elevation of the CEA. When the results of her CT scan were reviewed, her tumor had grown significantly and she was experiencing increased fatigue. She was referred to our oncology department for further evaluation.
In vitro studies were performed to examine the effect of fenbendazole on EMT6 cell viability. High doses of fenbendazole inhibited cell viability in both a standard colony formation assay and a more rigorous clonogenic assay. These data suggest that fenbendazole has both cytostatic and cytotoxic effects on these cells at high concentrations and long incubations.
In vivo experiments were also performed to examine the effect of fenbendazole alone and in combination with radiation on tumor growth and radiation response in mice. Mice were randomly assigned to three groups where they received either a fenbendazole-containing antihelminthic diet, a control diet or a fenbendazole-containing diet in combination with 10 Gy of x-rays. Tumor volumes were measured daily and time to tumors growing from the stratification volume to four-times that volume was calculated (Table 1). The results of these experiments indicate that fenbendazole, when administered alone or in combination with radiation, did not alter tumor growth or radiation response. This finding is consistent with our previous observations that fenbendazole, which is a methyl [5-(phenylsulfanyl)-1H-benzimidazol-2-yl] carbamate and is used as an antiparasitic agent, acts by binding to tubulin and disrupting the microtubule equilibrium in helminths, thus killing them without damaging mammalian host cells. fenbendazole cancer