Mice remained cancer free for as long as they took the drug. The drug also turned cancer cells back to normal.

Cancer experts said the Nature study held promise for human cancer drugs.

Cancer switch

The findings might also apply to cancers of the breast, bowel and prostate, the researchers hope.

This is because all of these cancers, as well as liver cancer, begin in cells that line the body called epithelial cells.

According to Cancer Research UK, the gene may contribute to as many as one in seven cancer deaths.

The Stanford scientists studied mice whose liver cells had been altered to carry a modified Myc gene known to cause cancer.

Myc controls cell division. Unlike the normal version of the gene, the modified version stayed permanently switched on, meaning cells were constantly dividing and some became cancerous.

Feeding the mice the antibiotic doxycyline turned the faulty Myc gene off so cancer growth was blocked.

When the researchers stopped the doxycycline the mice developed aggressive liver cancer.

Reintroducing doxycycline into their feed not only turned Myc back off, blocking further cancer growth, but it also turned the cancer cells back to normal.

Reversing cancer

Lead researcher Dr Dean Felsher said: "The exciting thing is you can turn cancer cells into something that appears to be normal."

But he said even though the cells looked normal, they still had the ability to become cancerous if the antibiotic were to be stopped.

This could explain why some cancers come back after people have had chemotherapy, he said.

"This is a terrible cancer. Anything that is encouraging in liver cancer may be important," he said.

Dr Elaine Vickers, science information officer for Cancer Research UK, said: "The Myc gene is known to be overactive in many types of cancer.

"Estimates suggest that the gene may contribute to as many as one in seven cancer deaths.

"This research is very interesting.

"It adds to the weight of evidence suggesting that drugs blocking Myc might be effective cancer treatments in the future."

http://news.bbc.co.uk/2/hi/health/3726124.stm