Your gut is home to tens of trillions of bacteria. Collectively, they act as another organ, one with many different roles. They influence your body weight, your ability to digest your food, your risk of catching infectious diseases, your chances of resisting infections or autoimmune diseases, the development of your brain, and more.

Now, we can add an entry to this growing list. At least in mice, gut bacteria can influence whether cancer treatments work.

Working independently, two teams of scientists showed that three cancer treatments rely on gut bacteria to mobilise the immune system and kill tumour cells—not just in the gut, but also in the blood (lymphomas) and skin (melanomas). Remove the bacteria with