By Emma Young

The idea that stress increases the risk of breast cancer is a persistent one, despite a number of major large-scale findings to the contrary. “Over the past 40 years, women have been exposed to strong messages about the importance of ‘thinking positively’ and reducing stress in their lives, which can add to the burden of guilt in those who develop cancer, who feel they have somehow failed”, note the authors of a new prospective study of women in Australia, published in Psycho-Oncology. Their findings suggest that neither acute nor chronic stressors recorded over a three-year period influenced the likelihood that a woman with a strong family history of breast cancer would develop the disease over the next three years.

“Our results, based on rigorous methodology, add to the growing literature providing reassurance to women at increased risk of breast cancer, who are concerned that the (often unavoidable) stressors in their lives may increase their risk of breast cancer”, the researchers said.

The team led by Phyllis Butow at the University of Sydney recruited 2,739 women from 990 families via a centre for research into familial breast cancer. Some of these women had genes that are known to increase the likelihood of developing breast cancer whereas the others did not, although there was an unusually high number of breast cancer cases in their family. At the start of the study, none of the women had ever been diagnosed with the disease.

On enrolment, the women were interviewed by a researcher over the phone, to collect details of any acute and chronic stressors they’d experienced over the past three years. Independent raters later rated these stressors as either acute or chronic; mild, moderate or severe; and noted their duration (for example, the death of a spouse was considered a severe acute stressor; moving home was a moderate acute stressor; caring for a handicapped child was a severe chronic stressor; a neighbourly dispute was rated as a moderate chronic stressor).

The women also completed questionnaires that measured their levels of social support, optimism, anger control, “anti-emotionality” (emotional stunting), and also anxiety and depression (the researchers measured and adjusted for anxiety and depression because of their potential influence on the self-reports of stressors and the psychosocial variables).

The interviews and questionnaires were repeated at three-yearly intervals for another 12 years, though only a few women completed all of the follow-ups. During the study period, 103 of the women were diagnosed with breast cancer. The researchers analysed the data to see if moderate/severe acute or chronic stress, or the psycho-social variables (adjusting for anxiety and depression), were associated with a subsequent increased risk of being diagnosed with cancer, but in fact none of them were (there was a trend for chronic severe stress to increase risk of diagnosis, but this was statistically non-significant).

The researchers argue that the study overcame methodological limitations of some other studies, in that, for example, there were objective ratings of various different kinds of stressor, and these stressors were assessed before diagnosis, rather than being reported by women after diagnosis.

It is in theory possible that stress did have an influence on breast cancer risk, but it was so small, compared with the genetic influences on the particular women in this study, that it couldn’t be detected. Also, while the results may not generalise to women in the general population, the researchers note that “internationally, most rigorous studies have also failed to find an association between psychosocial factors and cancer” (for example, check out the meta-analysis we covered last year). However, there are some conflicting findings, including those from a study of Finnish twins published in 2003 that found severe negative life events, like divorce, were associated with an increased risk of breast cancer.

Still, the researchers concluded: “Given the lack of evidence for an association between stressors and psychosocial factors and [breast cancer], we suggest that women at increased risk of [breast cancer] focus on proven methods of risk reduction such as close monitoring, risk-reduction medication, or, for those at high risk, surgery.”

—Does stress increase risk of breast cancer? A 15‐year prospective study

Emma Young (@EmmaELYoung) is Staff Writer at BPS Research Digest