Fenbendazole is a benzimidazole anthelmintic drug with a broad antiparasitic spectrum used in several animals and reported to exhibit antitumor effects by binding to b-tubulin microtubule subunits and disrupting tubulin polymerization. Increasing evidence suggests that the drug also may have direct cytotoxic activity in cancer cells, and a combination with taxanes or other chemotherapy agents may enhance treatment efficacy.

In a mouse model, fenbendazole reduced the viability of EMT6 tumors by both preventing cell proliferation and blocking the entry of nutrients. A more recent study found that high concentrations of the drug had cytostatic as well as cytotoxic effects in these cells, and it was effective in reducing their growth rate after radiation. These studies were performed using rigorous colony formation assays to evaluate the clonogenicity of tumors, and the time needed for each tumor to grow from its initial volume to four-times that volume was compared among groups.

A patient with advanced nonsmall-cell lung cancer received pembrolizumab monotherapy and developed severe liver injury 9 months later. Interviews with the patient and her family revealed that they had been taking oral fenbendazole (marketed as an anthelmintic for dogs) since early 2019, based on social media reports suggesting that this medication was effective against cancer. After the patient discontinued fenbendazole, her liver function returned to normal.  fenbendazole stage 4 cancer