Chemo 'may harm brains of patients'.
The 5-fluorouracil drug, known as 5-RU, destroyed brain cells which keep the nerves in working orders when given to laboratory mice.
It could explain why patients given chemotherapy sometimes complain of "chemo brain" - memory loss, poor concentration and even seizures, impaired vision and dementia. In the past, they have been dismissed as due to fatigue, depression and anxiety.
Dr Mark Noble, of the University of Rochester Medical Centre, New York State, said: "It is clear that, in some patients, chemotherapy appears to trigger a degenerative condition in the nervous system."
His team said that at least 82 per cent of breast cancer patients reported mental impairment after chemo. Martin Ledwick, of Cancer Research UK, said: "This research has taken place on mice and stem cells so it does not necessarily equate to real people's experiences."