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The idea that a woman's personality traits can make her more prone to breast cancer appears to be nothing more than a myth, according to a Dutch study.
Women who were unemotional, depressed or anxious were no more or less likely to get breast cancer than any other
women, the study found.
Nor were women who were optimistic, angry or understanding, or had any combination of personality traits.
The Dutch researchers measured 11 personality traits in 9705 Dutch women in a survey in 1989 and 1990, then tracked them through 2003 to see who got breast cancer.
"The present results indicate that women should not worry about a possible impact of personality factors as a risk factor for breast cancer," said Eveline Bleiker of the Netherlands Cancer Institute and Antoni van Leeuwenhoek Hospital in Amsterdam, who led the study.
"Moreover, women with breast cancer should not worry that their character might have contributed to the development of their disease."
She noted that some researchers in the 1980s advanced the idea of a "cancer-prone" personality with such traits as stoicism and difficulty in expressing emotions.
"The earlier studies had a number of methodological flaws," Dr Bleiker said, adding that more recent, large studies have not found the existence of a "cancer-prone" personality.
"In summary, there is currently no convincing evidence that such a personality profile exists."
Previously, Dr Bleiker's team studied the same group of women and found that one of the 11 personality traits, what they called "anti-emotionality", was associated with a slight increased risk for breast cancer.
But after tracking the women for a longer time in the new study, this association vanished.
This suggests it may have been a chance finding, Dr Bleiker said.
Women with the "anti-emotionality" trait responded negatively to survey questions such as: "In important situations, I trust my feelings," "I respond emotionally to people," and "my behaviour is influenced by my emotions."
New Zealand Cancer Society medical director Dr Chris Atkinson said it was a helpful, well-conducted study. "There's a lot of women that they've followed, so you would've expected to have enough breast cancer events in a population of 9000 women to have seen some sort of association if one was to be found.
"I think it's a good result for women because it emphasises that you don't bring these things on yourself.
"It's very easy to sometimes blame yourself if you get a cancer and in not many circumstances is there a true poor lifestyle choice which led to it."
Dr Atkinson said exercise, sensible diet, not smoking and not being too overweight were proven factors in reducing the risk of developing cancer.
Kevin Stein, a researcher at the American Cancer Society who was not involved in the Dutch study, said it was inappropriate and factually incorrect to blame a woman's personality for her breast cancer.
"I am pleased to see this stuff knocked down," Stein said. "There's really no support for the idea that your personality or your attitude can either cause a cancer or prevent or help avoid a cancer."
Cancer experts often work to shoot down various cancer myths. Among other misconceptions about cancer, the American Cancer Society debunks the idea that using underarm deodorants or antiperspirants can increase breast cancer risk, or that wearing under-wire bras raises the risk for breast cancer.
- Additional reporting by Errol Kiong
