During World War I, one of the horrors of trench warfare was a poisonous yellow cloud called mustard gas.
For those unlucky enough to be exposed, it made the air impossible to breathe, burned their eyes, and caused huge blisters on exposed skin.
Scientists tried desperately to develop an antidote to this vicious weapon of war.
In the process they discovered the gas was irrevocably damaging the bone marrow of affected soldiers — halting its ability to make blood cells.
Despite these awful effects, it gave scientists an idea.
Cancer cells share a characteristic with bone marrow: both replicate rapidly.
So could one of the atrocities of war become a champion in the fight against cancer?
Researchers in the 1930s investigated this idea by injecting compounds derived from mustard gas into the veins of cancer patients.
It took time and trial and error to find treatments that did more good than harm, but by the end of World War II, they discovered what became known as the first chemotherapy drugs.
Today, there are more than 100.
