Scientists say the plant from which it is derived may help cure cancer.

Tapioca is derived from the cassava plant.

It is one of many plants which manufactures cyanide to deter animals who might want to eat it.

It does this by producing a chemical called linamarin which releases hydrogen cyanide when it is broken down by the linamarase enzyme.

Geneticists at Newcastle University have been taking genetic material from the cassava plant and adding it to a virus.

This is then introduced into cancer cells which have been impregnated with linamarin from the cassava plant.

The aim is for the cancer cells to produce hydrogen cyanide in high enough doses so that they commit suicide.

Hydrogen cyanide

Professor Monica Hughes has been studying cassava and cancer for seven years.

She has cloned the genes from the plant which are responsible for producing hydrogen cyanide.

Her objective is to reduce the toxicity of the cyanide so that it will not harm humans.

Cassava is a staple crop for many people in Africa, Asia and South America, but, if it is processing wrongly, it can lead to cyanide poisoning.

Because the plant is rarely used in Western diets, it has not been subject to much scrutiny by geneticists.

Professor Hughes has been working with a research team in Madrid to modify the cassava gene and transfer it to a retrovirus.

This gives the retrovirus the ability to produce linamarase.

The Spanish researchers found that a brain tumour in a rat was totally eradicated after one week of the genetic treatment.

It allowed the localised release of small doses of cyanide through the breakdown of linamarin by linamarase.

Neighbouring cells

The team found that part of the reason the tumour was so quickly destroyed was that the cells containing the retrovirus also affected surrounding cells.

They say tests on human tissue samples for certain cancers also look promising.

Professor Hughes' research has been funded by the European Union, but her funding has now run out and she is looking for other sources.

She says her next step is "to modify the genetic material with a view to making the treatment more effective when applied to mammalian cells".