Fenbendazole for cancer, yeah or nay?

The short version: the evidence for fenbendazole as a cancer treatment in humans is essentially absent, and the only published human case shows liver injury with no tumor response.

The evidence you retrieved contains exactly one human case report [2]. An 80-year-old woman with advanced lung cancer took 1 gram of fenbendazole daily for three days on, four days off, for 30 days. Her liver enzymes shot up (AST from 24 to 386, ALT from 16 to 487) and her tumor did not shrink. The Naranjo score of 6 means the drug was a probable cause of the liver injury. That is the only human data you have. The other two studies are irrelevant to your question: one is a veterinary study of cattle parasites [3], the other is a lab-bench transport assay on drug pumps [1]. Neither tests fenbendazole against cancer in humans.

The mechanism that gets promoted online—that fenbendazole disrupts microtubules in cancer cells—is plausible in theory, but plausible is not proven. No controlled human trial has been published. No safety data beyond that single case exists. The burden of proof is on the intervention, and the evidence does not come close to meeting it.

My call: do not take fenbendazole for cancer. The only human evidence shows liver toxicity without benefit. Confidence: high, because the evidence base is not thin—it is nonexistent for efficacy and negative for safety in the one published case.