Swedish research presented at the eighth European Breast Cancer Conference (EBCC-8) in Vienna today (Wednesday), shows women over 50 with denser breast tissue have a higher risk of cancer recurrence.

A mammogram gives physicians an image of the breast, showing contrasts of white and black. The white areas represent the dense tissue, called epithelium and stroma, where cancer can more easily develop. The black areas are fatty tissue, which is not dense. The percentage density (PD) of the breast is effectively the dense area divided by the area of the whole breast (dense and non-dense tissue included).

Dr Louise Eriksson and her colleagues from the Karolinska Institutet (Stockholm, Sweden) have shown in their research that women with more dense tissue, had almost double the cancer recurrence risk than women with less dense tissue. The cancer generally reoccurred in the same breast or in the surrounding lymph nodes.

Dr. Eriksson explains that breast density varies from woman to woman, and it also decreases with age:

“Density can vary greatly, even between postmenopausal women. In the group of women I studied, those with the lowest percentage density had breasts that were less than one percent dense, whereas those with highest PD had 75-80% dense breasts. The mean average PD was 18%. However, density does decrease with age. Studies have shown a decrease by approximately two percent per year. The largest decrease is seen at menopause when PD decreases by approximately 10%.”

Dr. Eriksson who is a PhD student at the Karolinska, as well as a physician at the Stockholm South General Hospital, studied mammograms and outcomes for nearly 2000 post-menopausal women between the ages of 50-74. They were part of a larger study of all women with breast cancer diagnosed between 1993-1995 in Sweden. She continues that:

“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%. 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.”

“Our study shows that breast density before or at diagnosis should be taken into account even after diagnosis, for instance, when deciding on adjuvant treatment and follow-up routines; perhaps women with dense breasts should be followed more frequently or for a longer period of time in order to quickly spot any local recurrence.

“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. Our study confirms the importance of taking breast density into account in the screening setting.”

To date, scientists and doctors had little information about the relationship between density and tumors. The research results available were generally conflicting and inconclusive. Dr Eriksson’s study is important not only for its findings, but because it is seen as comprehensive, covering around 50% of all breast cancer patients in those years.

It’s not widely understood why an increase in density should increase the cancer risk, one idea has more cells simply meaning more area for cancer cells to develop in. Another shows that the interaction between stroma cells and epithelial cells plays a crucial factor in the development of cancer.

Professor David Cameron, from the University of Edinburgh (Edinburgh, UK), 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.”

Dr Eriksson concludes :

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.”

Written by Rupert Shepherd