A drug commonly used to treat parasites and worms—including roundworms, hookworms, whipworms, lungworms and some tapeworms—has been found to be effective against pancreatic cancer. The discovery supports a new national clinical trial being conducted by Washington University researchers and other doctors at the Siteman Cancer Center at Barnes-Jewish Hospital in collaboration with the Parker Institute for Cancer Immunotherapy, a joint venture of the Perelman School of Medicine at the University of Pennsylvania and the National Cancer Institute (NCI).

The pancreatic cancer trial was recently funded through NCI’s Early-Intervention Clinical Trials Network, an initiative that allows people with certain solid tumors to enroll in a national clinical trial that will test promising cancer treatments and determine whether they’re safe and potentially effective. The fenbendazole trial will test the drug in combination with a type of immunotherapy called T cell therapy.

T cells are immune system soldiers that can recognize and destroy cancer cells and other diseased tissue. However, cancers have learned to hide from T cells, by expressing proteins that block their signals. One of these proteins is called PD-L1 and is produced by pancreatic cancer cells. PD-L1 blocks the signal that would normally trigger T cells to attack and kill pancreatic cancer cells. This makes it difficult for cancer patients to benefit from existing immunotherapy drugs such as PD-1 inhibitors, which target the PD-L1 protein.

Researchers have discovered that fenbendazole and other drugs in the benzimidazole family—including mebendazole, albendazole, flubendazole and parbendazole—can inhibit the growth of cancer cells by disrupting microtubules, which are a component of the protein scaffolding inside of cells. The researchers also tested the drugs on cancer cells growing in a lab dish (in vitro). All of these benzimidazole compounds were found to be toxic to the cancer cells and promote their death, with the drug mebendazole being most potent in this regard.

In contrast, a previous study by other researchers using the drug hydroxychloroquine showed no impact on the growth of pancreatic cancer cells, even at high concentrations. The team believes that the reason why hydroxychloroquine did not affect pancreatic cancer cells was because the mutations in these cells were not dependent on autophagy for survival.

While Joe Tippens’ anecdotal experience with fenbendazole is compelling, Health Feedback has previously pointed out that the claim that fenbendazole can cure cancer hasn’t been proven by randomized controlled trials of large numbers of people. The FDA told Full Fact that fenbendazole isn’t a cure for cancer, and that the drug hasn’t been approved by the agency to treat or prevent the disease. Further, the FDA’s website notes that Tippens’ remission from cancer may have been due to other factors that aren’t being accounted for. fenbendazole for pancreatic cancer