This latest research contradicts earlier findings linking high-stress incidents to breast cancer.

The new conclusions, published in the Lancet and the British Medical Journal suggest that psychological factors have no significant bearing on the disease.

The only exception was that women who felt that the situation was "hopeless" generally fared worse than others.

Women who think the situation is hopeless may do worse

The first study looked at stressful life events such as bereavements or divorce, and examined whether this meant women were more likely to have a benign breast lump or a cancer when coming to a clinic.

It found that such events were common - at least two-thirds of women had suffered one in the five years approaching their diagnosis.

And it concluded that, statistically, stressed women were no more likely to develop breast cancer.

'Stress makes cancer come back'

But Professor Amanda Ramirez, a consultant psychiatrist at the Imperial Cancer Research Fund, said: "This study shows that stressful life events do not 'trigger' cancer.

"However, this is not the same as saying that stress does not affect the growth of an existing cancer.

"Imperial Cancer Research Fund research suggests that stressful life events are associated with an increased risk of reccurrence."

The other survey took nearly 600 early diagnosis breast cancer patients at the Royal Marsden Hospital in London and asked them their attitude to the disease.

A total of 166 women were classed as having "fighting spirit", in that they took a more positive approach to the disease, perhaps seeing it as a challenge rather than a burden.

No signs of a benefit

However, this had no bearing on the outcome of their illness, according to researchers.

The only instance in which mental state appeared to affect outcome was for those with the most negative thoughts - these appeared to worsen the chances of survival.

Dr Molly Watson, who led the study, said more research was needed to investigate why feeling helpless and hopeless appeared to reduce a breast cancer patient's chances of survival.

"One possible explanation is that their state of mind might influence their immune system or stress hormones which could have a negative effect on their health

"Another theory is that patients who feel helpless may be less motivated to make sure they get the best available medical treatment or take good care of themselves."

Jean King, the Director of Education at the Cancer Research Fund, said that hopefully women who felt they could not muster such a "fighting spirit" would not feel guilty or worry about their chances.