Scientists have shown they can turn off a cancer-causing gene in mice, offering hope of new treatments for cancer patients.
Liver cancer was blocked in mice
The Stanford University team used a drug to turn off a gene called Myc, which is known to trigger cancer.
Mice remained cancer free for as long as Myc was switched off.
Cancer experts said the Nature study held promise for human cancer drugs working on the same 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.
The researchers engineered mice so that the Myc gene could be switched off by a common antibiotic called doxycycline.
Feeding the mice 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.
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.
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."