(CORDIS) — Age and breast tissue play a significant role in whether breast cancer will recur, new Swedish research shows. Scientists at the Karolinska Institutet in Stockholm have discovered that the odds that patients will see their breast cancer return is higher in women who are aged 50 and over and who have breasts with a high percentage of dense tissue. The results shed a great deal of light on the link between density, tumour characteristics and prognosis. No other study has succeeded in doing so. The findings were presented at the 8th European Breast Cancer Conference (EBCC-8) in Vienna, Austria on 21 March.
Led by Dr Louise Eriksson from the Karolinska Institutet, the researchers identified that there is a 50% greater risk of cancer recurring either in the same breast or in the surrounding lymph nodes of women with dense breast tissue compared with women who have less dense breasts. The team believes physicians must consider breast density when determining the best course of treatment for and follow-up of patients.
According to the researchers, scans generated via mammograms indicate white and black areas of breast tissue. The white areas are dense, consisting of the epithelium and stroma, and the black areas are composed of fatty tissue, which is not dense. Measurements to determine the breast’s percentage density (PD) were made by dividing the dense area by the area of the entire breast, including dense and non-dense tissue. They found a connection between age and density: breast density shrinks with age.
‘Density can vary greatly, even between postmenopausal women,’ Dr Eriksson said. ‘In the group of women I studied, those with the lowest percentage density had breasts that were less than 1% dense, whereas those with highest PD had 75% to 80% dense breasts. The mean average PD was 18%. However, density does decrease with age. Studies have shown a decrease by approximately 2% per year. The largest decrease is seen at menopause when PD decreases by approximately 10%.’
A total of 1 774 post-menopausal women between the ages of 50 and 74, and who were part of a larger Swedish study of all women diagnosed with breast cancer from 1993 and 1995, participated in this study.
‘We found that if you have a PD at diagnosis of 25% or more, you have an almost two-fold increased risk of local recurrence in the breast and surrounding lymph nodes than women with a PD of less than 25%,’ Dr Eriksson explained. ‘However, density does not increase the risk of distant metastasis and has no effect on survival. We also see that although mammographic density is one of the strongest risk factors for breast cancer, it doesn’t seem to influence tumour development in any specific way; for instance, it isn’t more associated with oestrogen receptor-positive tumours than oestrogen receptor-negative tumours, but seems to act as a general stimulator of tumour development.’
She went on to say that breast density before or at diagnosis must be considered even after diagnosis. It is probably a good idea to also follow up on patients with dense breasts for longer periods of time, the researcher suggested.
‘As far as screening programmes are concerned, it is already known that breast density is a risk factor for the occurrence of breast cancer and that it decreases the sensitivity of mammograms,’ she said. ‘Our study confirms the importance of taking breast density into account in the screening setting. Based on the results from our study, we propose that mammographic density creates a beneficial environment for epithelial cells to transform into cancer cells; much like fertile soil giving a planted seed the needed nutrients to grow and develop.’
Commenting on the results, Professor David Cameron of the University of Edinburgh in the United Kingdom, and chair of EBCC-8, said: ‘This study raises questions about how and why the appearance of normal breast tissue on a mammogram could influence the chances of a local recurrence of breast cancer. It is, therefore, more thought-provoking than practice-changing, since it is not clear what a patient, or her physician, should do if the mammogram shows a higher density of the normal breast tissue. A number of factors are known that influence mammographic breast density, but more research is needed to know which of these, if any, is responsible for this important observation.’