Not to mention, we aren't exactly sure how many commonly used / prescribed drugs work. Acetaminophen, for example - we have theories, we know it inhibits COX enzymes, maybe metabolite interactions with endocannabinoid receptors, but we don't exactly know how it relieves pain. We're not sure how lithium stabilizes moods, or how inhaled anesthetics cause you to lose consciousness. We know Metformin halts the liver's production of glucose but we're not sure how. Not at all uncommon for drugs to be used in medicine without knowing their exact mechanism. If a drug works and is proven safe through testing obviously we should use it, especially I think for something like cancer.