Sure, but there are far more things which will kill the entire person at the same dose they'll kill the cancer than things which can be carefully controlled by choosing the right dose.

These studies which claim to kill cancer in a petri dish usually turn out to be the former, because not killing the host is the difficult part

If you swallow a bunch of gunpowder, drink gasoline, fill yourself with nitroglycerin, and then slam yourself on the floor—sure, you'll get hired by the talent agent, but then you have to reveal that you can only do the trick once.