Certain things in the world around us, such as tobacco smoke, cause cancer. They do this by triggering chemical changes inside cells, leading to errors in the reading of the DNA genetic code.

The patterns of these DNA changes are different for each cause (or ‘carcinogen’) – almost as if they are signing their names on our genomes – and scientists can identify known carcinogens from their chemical signatures.

But there are unusual signatures whose origins we don’t know, caused in ways we haven’t yet identified. And in cancers caused by factors such as obesity, there will be many different signatures, and we don’t yet know how to pick them apart.

So in the same way that a detective uses forensic evidence from a crime scene to identify a criminal, we need to work backwards to find these cancer-causing events, to prevent the cancers they’re causing.