The latest technique allows doctors to incorporate results from far more recent years.

This means that advances in treatment and detection which improve the chances of patients are taken into account.

Timely detection of improvements in long-term survival rates might help to prevent clinicians and their patients from undue discouragement

Researchers writing in the Lancet

A study in the Lancet looked at figures for cancer survival in the US between 1973 and 1998.

Normally, statisticians take a group of patients diagnosed in a particular year and follow their progress.

Five, 10 and 20 years later they check to see how many are still alive - and calculate survival rates from this.

However, to get a 20-year survival prediction from these figures would involve taking a group of patients diagnosed in 1978.

Breakthroughs

Cancer treatments have advanced greatly since then - but the figure takes no account of this.

As a result, cancer doctors often will not give any more than a five-year-survival rate to their new patients, and this is unsatisfactory, particularly in cancers such as breast where this figure does not always correspond with 10-year and 20-year survival.

The new method, devised by statisticians in Germany, however, does manage to take account of more recent advances - yet can offer a 10-year and even a 20-year estimate.

The net result when applied to the US figures was to boost up survival figures for many cancers.

On average, while five-year survival rates were only 1% higher, 10-year rates were 7% higher, and 20-year rates 11% higher.

Pessimism cut

The researchers wrote: "Timely detection of improvements in long-term survival rates might help to prevent clinicians and their patients from undue discouragement or depression by outdated and often overly pessimistic survival expectations."

A spokesman for Cancer Research UK said it would allow patients diagnosed with cancers a more accurate view of their prospects.

She said: "We have always been reluctant to give out anything more than a five-year survival rate - but patients are obviously very interested in more long-term survival.

"We have commissioned some work which will look at the UK data using this method."