That makes sense. I think most people underappreciate how polyclonal cancer is. Every tumor isn't one cell, it's dozens or hundreds of different types of cell, which makes it extremely hard to cover all the possible escape paths for the cancer overall. As you mention, going with a shotgun approach of different drugs can help, but that's when toxicity becomes a real problem. It's not always possible to just give 2 drugs because one is so toxic on its own so you might kill the patient. One of the theories I've heard about why we've made relatively more progress on cancers in children is that they "heal" better, which means they can actually tolerate higher doses for some of these drugs.