Prof Shankar Balasubramanian and colleagues at Cancer Research UK`s Cambridge Research Institute says the naturally occurring molecule -- thiostrepton -- "clamps" on to a cancer-causing protein called FOXM1, preventing it from working.
The scientists say that one of the main challenges is to stop the cancer before it spreads to other parts of the body, making it far harder to treat. But, they now hope that a drug could be developed to mimic the molecule, which was first discovered in bacteria, a newspaper reported.
In fact, according to the scientists, breast cancer cells show increased levels of FOXM1. It attaches to certain areas of DNA and turns on genes which regulate the growth and division of cells, producing tumours.
It then causes those tumours to spread, even triggering the growth of blood vessels to supply them with nutrients.
Although designing drugs is a huge challenge, the discovery will pave the way for creating molecules which mimic thiostrepton but are even more effective at blocking the effects of FOXM1.
"This naturally occurring molecule doesn`t have all the right properties to be used as a treatment itself. But this exciting discovery paves the way for the design of more potent and selective drugs based on the structure of thiostrepton," Prof Balasubramanian said.
Added Dr Lesley Walker of Cancer Research UK: "Survival rates for breast cancer have been improving for 30 years thanks to more targeted treatments. It`s fascinating to discover how simple bacteria could hold the key to powerful new approaches to stop breast cancer spreading."
Experts have hailed the findings published in the `Nature Chemistry` journal.
Dr Rachel Greig, of Breakthrough Breast Cancer, said: "This work may also open the door for other molecules to be investigated which could also have cancer blocking potential."