Women with breast cancer often consider stress as a likely cause of their disease, but in the largest study to date of the potential link between psychological stress and breast cancer, no association has been found.
The finding comes from the Breast Cancer Now Generations Study, a landmark prospective study of the causes of breast cancer, which will follow more than 113,000 UK women for 40 years. In a new analysis, scientists at The Institute of Cancer Research, London – led by Dr Minouk Schoemaker and Professor Anthony Swerdlow – investigated whether stress affected breast cancer risk.
Results of the study
When participants entered the study, from 2003 onwards, they were asked how frequently they had experienced stress and whether they had experienced any of eight different types of stressful event over the past five years, such as bereavement or divorce, with an additional question about the loss of a parent under the age of 20. The study then followed the participants for an average of six years to see how many of them went on to develop breast cancer.
The study also collected data from participants concerning other breast cancer risk factors, such as obesity, physical activity, alcohol consumption, family history of breast cancer, age at first period and menopause, number of children and the woman’s age at their births, and duration of breastfeeding. This meant the scientists were able to control for the influence of other risk factors to separate out any potential effects from psychological stress. This information, combined with the large study size and information collected about the types of breast cancer that women developed, makes the study particularly powerful.
The results showed that one in three women (34%) reported frequent or continuous stress over the preceding five years and three out of four (74%) reported at least one adverse life event, such as bereavement or divorce.
Some 1,783 of the 106,612 women followed up went on to develop breast cancer. Having controlled for all other breast cancer risk factors, no statistically significant association between frequency of stress and overall breast cancer incidence was found.
For seven of the eight types of stressful event, no adverse effects were found on breast cancer risk. The researchers observed a weak association between oestrogen receptor negative breast cancer and divorce, but this was based on just 25 cases and was of only borderline statistical significance. The association was not supported by other evidence from similarly stressful events – including bereavement – and is therefore likely to be a chance finding.
The analysis also found that breast cancer risk was raised in women who were younger than 20 when they lost their mother. However, this effect was not statistically significant after mothers who had had breast or ovarian cancer were excluded, suggesting that this increase in risk was at least partly down to genetic predisposition rather than the effects of bereavement itself.
The Generations Study
As the Breast Cancer Now Generations Study is designed to follow women over 40 years, collecting updated lifestyle information from participants and monitoring which women go on to develop breast cancer, researchers will be able to repeat this analysis in the future with an even larger number of breast cancer cases over a longer time period.
The Breast Cancer Now Generations Study was launched in 2003 to help understand the causes of breast cancer. While it is known that one in eight women will be diagnosed with the disease in their lifetime, a clearer understanding of the causes of the disease is needed in order to identify those women who are most likely to develop it, and find the most effective ways to reduce their risk.
Study leader Dr Minouk Schoemaker, Staff Scientist at The Institute of Cancer Research, London, said:
“It’s always a challenge to try to disentangle which of life’s many experiences and behaviours might influence the risk of cancer. Our study has analysed very large amounts of data from women over many years, and has provided good evidence that stress is unlikely to increase the risk of developing breast cancer.
“Stressful life events are common and many women will have experienced them in the run-up to being diagnosed with breast cancer, but our results suggest that those stressful events are unlikely to be the cause of the disease.”
Baroness Delyth Morgan, Chief Executive at Breast Cancer Now, said:
“Many women often question whether their breast cancer could have been triggered by stress or a particularly difficult experience. This ground-breaking study provides the most robust evidence to date that stress itself is unlikely to be a biological cause of the disease.
“As the Breast Cancer Now Generations Study continues to uncover more about the underlying causes of the disease, we need to turn this into practical guidance to help women reduce their risk.
“What we already know is that simple steps such as maintaining a healthy weight, lowering alcohol intake and being more physically active can help women lower their risk of breast cancer.
"It's important to remember that age and gender remain the most significant risk factors for breast cancer, which women cannot do anything about, and continued research into better diagnosis, treatments and support is therefore critical."
Breast Cancer Now thanks M&S for their generous support of the Breast Cancer Now Generations Study. This research was also supported by NHS funding to the Royal Marsden and The Institute of Cancer Research NIHR Biomedical Research Centre.