Modern medicine has made significant advances in cancer treatments over the decades. But all cancer therapies still face one critical challenge: how to target cancers without damaging healthy cells.

Imperfect solutions lead to side-effects: surgery and radiation can damage nearby healthy tissue, while chemotherapy can indiscriminately target fast-growing cells, damaging healthy hair follicles and stomach lining.

An alternative approach involves recruiting a surprising ally: bacteria. Some species of bacteria cannot survive in the presence of oxygen. They live in low-oxygen environments such as deep in the soil or at the bottom of lakes. These so-called anaerobes are generally unable to infect healthy tissues, in which oxygen is abundant.

In contrast, cancerous tumours are not well-oxygenated. As tumours grow, their blood supply becomes abnormal and inefficient, leading to poorly oxygenated regions in the tumour interior. This low oxygen environment provides a unique niche for an anaerobic bacterial infection.

To employ these bacteria in cancer therapies, doctors could inject a patient with dormant spores of an anaerobe. Those spores would travel the bloodstream and remain inert in healthy oxygenated tissue. When spores find their way into tumours, they can initiate self-limiting infections that could suppress the........

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