Animal testing is used for some initial toxicology and indicators that a treatment is worth testing in humans but you can't use animals to "prove" a treatment i

Animal testing is used for some initial toxicology and indicators that a treatment is worth testing in humans but you can't use animals to "prove" a treatment is effective for people. Once a treatment is through animal safety trials, they will give it to patients with very advanced stages of cancer, who are considered unlikely to survive very long. This is both to minimize harm, and make it easier and cheaper to tell whether a treatment worked.