A key tumour survival mechanism identified by scientists may help to explain how some cancers bounce back after chemotherapy.

The research shows that cancer can reverse a natural self-destruction process that commits normal cells to die.

Programmed cell suicide, or apoptosis, allows the body to rid itself of damaged and potentially dangerous cells.

The Chinese scientists treated human cervical, skin, liver and breast cancer cells with three different chemicals which initiate apoptosis.

Normal cells that are driven to suicide reach a "point of no return" after which they have to die, even when the death trigger is removed.

But the researchers found that cancer cells crossing this point were still able to recover once the suicide-inducing chemicals had been taken away.

The cells regained their shape and function and continued to divide. They only failed to survive once the nuclei containing the bulk of their DNA began to disintegrate, an event right at the end of the cell suicide process.

Professor Ming-Chiu Fung, from the Chinese University of Hong Kong, said: "We have shown that various cancer cell lines can survive programmed cell death. This research suggests the existence of an escape tactic which cancer cells might call upon to survive chemotherapy treatment.

"Our finding sparks new leads to research what drives cancer cells to come back to life after chemotherapy treatment. Or to what extent this ability of cancer cells to reverse cell death contributes to their continued division and growth during cycles of anticancer treatment. Answers to these questions will provide potential new therapeutic targets in our battle against cancer."

The findings were reported today in the British Journal of Cancer.

Dr Lesley Walker, information director at Cancer Research UK, which publishes the journal, said: "This eye-opening discovery has created an entire map of new routes to explore in the search for new therapy targets. It is an intriguing advance and one that we hope will play a useful part in our efforts to beat cancer."