“Menopausal women with hot flushes are half as likely as others to develop breast cancer,” reported the Daily Mirror . It said that the “sweating attacks are caused by a lack of the hormone oestrogen – but the shortfall may also cut the risks of getting tumours”.
This news story is based on a study that analysed information about women’s menopausal symptoms from about 1,000 postmenopausal women with breast cancer and 500 similarly aged controls without the disease. The main limitations are that women had to recall their past symptoms, and that some of the individual groups that were compared were relatively small.
Overall, a link between menopausal symptoms and the risk of breast cancer appears plausible, but larger prospective studies are needed to confirm whether this link exists and, if so, how strong it is. It is important to note the majority of women do experience some menopausal symptoms, even those who go on to develop breast cancer.
Where did the story come from?
The study was carried out by researchers from the University of Washington and the Fred Hutchinson Cancer Research Centre. Funding was provided by the National Cancer Institute. The study was published in the peer-reviewed medical journal Cancer Epidemiology, Biomarkers & Prevention.
The Daily Mail and Daily Mirror provide balanced coverage.
What kind of research was this?
This case control study investigated whether the symptoms that women experience while going through the menopause are associated with their later risk of breast cancer. The menopause is associated with lower oestrogen levels, while breast cancer has been linked with higher levels of the hormone. This has led the researchers to suggest that a woman’s menopausal symptoms might be related to their risk of breast cancer.
The ideal study design for investigating this question would be a prospective cohort study. However, such studies need to be quite large and are expensive. A case control study design is easier and cheaper to conduct, and is an appropriate way of initially investigating this question. The study design does have some limitations, in that exposures (in this case menopausal symptoms) were assessed in retrospect, and some people may not be able to recall their exposures accurately.
In addition, as the case and control groups (women with and without breast cancer) were selected by the researchers, they needed to be as similar as possible in terms of other factors that could affect the results, such as age or use of medication to treat menopausal symptoms.
What did the research involve?
The data used in this study came from an earlier case control study that had investigated the use of hormone replacement therapy and risk of breast cancer in women aged 55 to 74. The study identified postmenopausal women from this study who had breast cancer (cases), and matched these to a similar group of women without breast cancer (controls).
As well as assessing use of hormone replacement therapy, the women were asked whether they had experienced symptoms such as hot flushes during their menopause. In the current study, the researchers then looked at whether menopausal symptoms were more or less common in cases than controls.
The study looked at menopausal symptoms and the risk of three different types of breast cancer:
- invasive ductal carcinoma (494 women)
- invasive lobular carcinoma (307 women)
- invasive ductal-lobular carcinoma (187 women)
Invasive ductal carcinoma and invasive lobular carcinoma are reported to be the two most common types of breast cancer.
The researchers looked at the risk of these three different types of breast cancer separately, because they appear to vary in their sensitivity to oestrogen, with invasive lobular carcinomas being more hormonally sensitive than invasive ductal carcinomas.
The researchers aimed to match each woman with breast cancer by age, within five years, to a control woman from the general population. The researchers initially contacted 9,876 households to identify potential controls. Women with missing data were excluded, as were those who did not participate for other reasons (such as a language barrier, or refusal to participate). This resulted in 660 eligible controls, 449 of whom were interviewed and included in the final analyses. This was less than half of the number originally intended.
All women were interviewed about their experience of menopause, reproductive and menstrual history, use of hormone replacements, family history of cancer, body size, medical history and alcohol consumption. The menopausal symptoms that were assessed included hot flushes, sweating (including night sweats), vaginal dryness, bladder problems, irregular or heavy menstrual bleeding, depression, anxiety, emotional distress and insomnia.
In the main analysis, women who had experienced any menopausal symptoms were compared with those who had not experienced such symptoms. Other analyses that were carried out included an assessment of the relationship between intensity of hot flushes and risk of breast cancer. The researchers considered factors that could affect results, including age, year of diagnosis, family history of cancer, type of menopause (natural or induced by medical treatment or hysterectomy), age at menopause, number of children, duration of hormone replacement therapy, body mass index and alcohol consumption. The final analyses took into account those factors that were statistically the most important and the odds ratio was adjusted for age, year of diagnosis, duration of hormone therapy use and the type of menopause.
What were the basic results?
Among the controls, 88.6% had experienced menopausal symptoms, compared with 80.6% of women with invasive ductal carcinoma, 81.8% of women with invasive lobular carcinoma, and 86.6% of women with invasive ductal-lobular carcinoma.
The researchers found that women who had experienced any menopausal symptoms were less likely to be at risk of two different types of invasive breast cancer than women who had not experienced any menopausal symptoms. They found that among the women who had experienced any menopausal symptoms:
- the odds of a diagnosis of invasive ductal carcinoma were reduced by 50% (odds ratio [OR] 0.5, 95% confidence interval [CI] 0.3 to 0.7)
- the odds of a diagnosis of invasive lobular carcinoma were reduced by 50% (OR 0.5, 95% CI 0.3 to 0.8)
These analyses took into account other factors that could have affected the results. The odds of women who had experienced menopausal symptoms developing invasive ductal-lobular carcinoma were not significantly different from women who had not experienced menopausal symptoms (OR 0.7, 95% CI 0.4 to 1.2).
When looking specifically at hot flushes, the more intense a woman’s hot flushes, the less likely she was to develop any of the three types of breast cancer being assessed.
How did the researchers interpret the results?
The researchers concluded that their study was the first study to report that women who have had menopausal symptoms are at reduced risk of breast cancer. They say that if their findings are confirmed, this could help understand the causes of breast cancer and factors that could be important for the prevention of breast cancer.
This study suggests that women who experience menopausal symptoms may be at less risk of breast cancer. There are a number of points to note:
- The study asked women about their menopausal symptoms retrospectively and there may be some inaccuracies in their recollections.
- The study was relatively small, which may reduce the reliability of results, particularly when comparing small subgroups of women, e.g. the different intensities of hot flushes.
- The authors note that there were high response rates among women who were asked to participate (71% for controls, 83% for cases). However, the actual number of controls who participated was low. If the women who agreed to participate differed from those who did not, this could affect results.
- The authors attempted to take into account several factors that could affect the results, particularly the duration of hormone therapy use, and the type of menopause. However, other unknown or unmeasured factors could be having an effect on the results.
- Although the link between menopausal symptoms and the risk of breast cancer was suspected to be related to oestrogen levels, this could not be confirmed because the women’s oestrogen levels had not been directly measured, only their menopausal symptoms were.
Overall, a link between menopausal symptoms and the risk of breast cancer appears plausible, but larger prospective studies are needed to confirm whether this link exists.