Arsenic is a poisonous metal that has long been linked to an increased risk of cancers, diabetes, thickening of the skin, diseases of the liver and digestive complications.

Now, the European scientists have unravelled the paradox of how the carcinogenic poison act as a treatment for cancer by watching the behaviour of the arsenic compounds in animal cells, The Guardian reported on Monday.

They found arsenic acts like glue, sticking itself to a type of molecule involved in leukaemia. This molecule, called Sumo, is then attacked by an enzyme called RNF4, a process that also destroys the cancer-causing proteins.

"Our discovery is key to understanding how we can enhance the anti-cancer properties of this poison. Knowing the specific molecules involved allows us to work on creating more targeted and effective cancer drugs with fewer side effects," lead researcher Ronald Hay of University of Dundee said.

Added co-researcher Michael Tatham: "People have been (trying) for the past 20 years to piece together how treating patients with arsenic results in the death of leukaemia cells. We have added a major piece to that puzzle."

The results of the study, which are published in the 'Nature Cell Biology' journal, has been welcomed by experts in this field.