A team of researchers at CIC bioGUNE has revealed that oestrogen can reduce the risk of breast cancer. Their work shows that oestrogen is capable of reducing the number of breast cancer stem cells, which may explain the lower aggression of the tumour and, as a consequence, the possibility of a better prognosis. The project was published in Breast Cancer Research and Treatment and the team will present the results under the auspices of the International Conference on Breast Cancer to be held in Madrid. The research combined the use of human samples and laboratory cell lines.

The identification of cancer stem cells (or tumour-initiating cells) has opened up a new perspective on breast cancer, with new hopes for treatment in the future. To date treatment against cancer was designed to reduce the mass of the tumour. Nevertheless, what has recently been discovered is that, while traditional treatment is capable of killing most of the cell mass of the tumour, the cancer stem cells are more resistant to common treatment such as chemotherapy and radiation. Thus, in order to cure the cancer with greater efficacy and definitively, it is important to find ways to eliminate cancer stem cells as well.

Oestrogen is a hormone which is not without its complexity; on the one hand it is essential for the normal development and functioning of the breast and, on the other, this same hormone induces the proliferation of cancer cells once the breast tumour has appeared, i.e. oestrogen is also a risk factor in breast cancer. However, nothing or little has been known until now about the effect of oestrogen on the tumour-initiating cells.

Over recent years highly important steps in the fight against breast cancer have been taken, notable enhancing its diagnosis, prognosis and possible treatment, giving rise to a very considerable increase in the survival rates of patients. It had also been proposed that the number of cancerous stem cells is correlated with the aggressiveness of the tumour: The greater the percentage of breast cancer stem cells, the greater the aggressiveness and the worse, thereby, its prognosis.

“To our surprise, what we have seen is that oestrogen reduces the proportion of breast stem cells which means a mechanism for explaining this better prognosis observed with tumours that express the oestrogen receptor. That is, those tumours expressing the oestrogen receptor are less aggressive, better differentiated and thus have a better prognosis”, explained Ms María Vivanco, leader of the research team.

Ms Vivanco believes that this study presents a new functional aspect of oestrogen, due to its capacity for acting in a different way depending on cellular type.

In the opinion of the CIC bioGUNE researcher, this study “has set out the molecular bases for understanding the direct effect of oestrogen on the proportion of stem cells, whether in healthy or cancerous tissue and the fact that the oestrogen receptor is an excellent prognostic marker”. Moreover, this means there is an explanation for a number of clinical observations, for example: the high levels of oestrogen in the blood of postmenopausal patients being associated with less aggressive tumours; the fact that little-differentiated tumours contain more cancerous stem cells, in turn associated with the degree of the tumour, the absence of the oestrogen receptor and low survival rate; and the observed benefit of lactation attributed to a greater differentiation in the breast.

The researchers consider that the new study represents a highly important step, opening new doors to developing tools for the prevention of breast cancer.