LONDON - British researchers have discovered how many mutations are needed for a normal cell to turn into a cancer cell. And the answer is: between one and 10 mutations, depending on the type of tumour.

Scientists at the Wellcome Trust Sanger Institute have addressed one of the most debated topics in cancer research for years.

Their findings, published in the journal Cell, showed that it takes just one mutation, for instance, to create thyroid and testicular cancers; four mutations to develop breast or liver cancer; and 10 mutations to drive colorectal cancer.

They studied the DNA from 7,664 tumours to find "driver mutations" that allow a cell to be more cancerous.

One of the researchers, Dr Peter Campbell, told the BBC News website: "We've known about the genetic basis of cancer for many decades now, but how many mutations are responsible has been incredibly hotly debated.

"What we've been able to do in this study is really provide the first unbiased numbers.

"And it seems that of the thousands of mutations in a cancer genome, only a small handful are responsible for dictating the way the cell behaves, what makes it cancerous."

The findings could pave the way for more targeted cancer treatment in the future.