In lab experiments, scientists found that the extract stimulated leukaemia cells to commit suicide.

Within 24 hours, 76% of leukaemia cells exposed to the extract were killed off, while healthy cells were unharmed, Clinical Cancer Research reports.

The study raises the possibility of new cancer treatments, but scientists said it was too early to recommend that people eat grapes to ward off cancer.

Anti-cancer drugs such as anthracylines are known to damage the heart - but Dutch researchers have shown that damage gets worse over the years.

They followed up 22 children and young adults treated with the drug doxorubicin for bone tumours.

The University of Groningen researchers say people who take the drugs should be given life-long cardiac monitoring. The study appears in Annals of Oncology.