TORONTO (CP) - What causes breast cancer? What keeps it from recurring? Medical science has some answers but it appears women who have survived the disease have ideas of their own.

A significant number of breast cancer survivors blamed stress for their disease and credited a positive attitude for their survival, a study published Wednesday reveals.

A team of Toronto researchers was startled to discover that factors for which there are proven scientific links - diet, environment, genetics and lifestyle - were not seen to be responsible for the development of breast cancer anywhere near as often as stress.

And only four per cent of survivors credited tamoxifen - an anti-estrogen drug used for high risk women - with their survival, while 60 per cent felt a positive attitude kept cancer at bay.

"I was surprised at the depth with which they held the feeling that stress and positive attitude would be so helpful," admitted Dr. Donna Stewart, lead author of the article which appears in the March issue of the journal Psycho-Oncology.

"Although I expected some people to say that, I didn't expect it to be number 1 and I didn't expect so many of them to endorse it."

The team surveyed nearly 400 breast cancer survivors, all of whom had been disease-free for at least two years and on average nine years. The women were recruited from a follow-up care program at Toronto's Princess Margaret Hospital and from breast cancer support groups across the country.

The women were asked what they believed caused their cancer and why they believed they had survived the disease. The questionnaire did not prompt the women to select their answers from a list of options. They were allowed to pick more than one factor for each question.

"It wasn't a forced choice. There were opportunities for them to put in anything they wanted to," said Stewart, a professor at the University of Toronto and chair of women's issues for the University Health Network, a group of affiliated Toronto hospitals.

On the question of cause, stress was named by 42 per cent of the women. That's well ahead of genetics (27 per cent), environmental factors (26 per cent), hormones (24 per cent) and diet (16 per cent).

There are studies suggesting all those factors - with the exception of stress - can contribute to the development of breast cancer.

In addition to positive attitude and tamoxifen, women credited their survival to: diet (50 per cent), healthy lifestyle (40 per cent), exercise (40 per cent), stress reduction (28 per cent), prayer (26 per cent) and complementary therapies (11 per cent).

"I think it's reflective of what's going on in society in general," said Stewart. "People think stress causes everything."

She said there have been some studies linking stress to suppression of the immune system and one small study that suggests women in breast cancer support groups are less likely to suffer a recurrence of the disease.

"The evidence for stress is pretty low. And. . .the evidence for hormones and genetics is pretty high."

A psychologist who works with breast cancer patients was not surprised that the study suggests women believe factors other than the standard medical explanations are at play with breast cancer.

Dr. Ross Gray works at Toronto Sunnybrook Regional Cancer Centre. In his work with cancer patients, many cite stress as a leading cause of their disease. And many believe limiting the stress in their lives can help their recovery, he said.

"I think for most people I've seen over the years who decide that having some kind of a positive attitude or alleviating stress in their lives as a response to having cancer, it overall works in their own best interests," he said in an interview.

He pointed to the fact that some studies have shown that psychological intervention seems to contribute to a longer survival time for people whose cancer has spread.

"So it's not that farfetched for somebody with cancer to realistically try and reduce stress and make their lives better in the hope it might help them."

Besides, cancer patients lose so much control over their lives while undergoing surgery, chemotherapy and the like that it's understandable that they might want to try to take back some control by exercising the belief they can have an impact on their survival, he said.

"Anything that helps you sense that here's something that I can do for myself that will probably help and here's a way of understanding it, it can be important."

Stewart said doctors treating women with breast cancer should address the issue of beliefs in treatment and should use what they learn to help frame the woman's treatment in a way that makes sense to her.

"I think it may be helpful for the doctor when they hear that kind of thing to say something like: 'Well, you know, the answers aren't all in, obviously. And if you can use that in a way that will help you to cope with this, then that's good. What are you doing, by the way, about your diet and your exercise?'

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