Bacteria and viruses generally bring unpleasant thoughts to mind: having the flu, maybe, or food poisoning. However, these little guys have a positive place in our lives, like the microbes in our gut that keep us healthy. Amazingly, they may also hold the key to the future of cancer therapy. While scientists generally study human diseases in mice, rats, or even monkeys, nature’s tiniest beings have special properties we can learn from and harness for cancer treatment. Let’s go on a journey through three such examples – showing that when it comes to biological capability, size doesn’t matter.