Oestrogen concentrations and breast cancer

• Oestrogen regulates the female menstrual cycle, and after menopause, a woman's chances of developing breast cancer increases. This is due to increased oestrogen concentrations. Once a tumour has developed, it further increases oestrogen concentration which leads to increased development of the tumour.
• Some white blood cells are drawn to breast cancer tumours, further increasing oestrogen concentrations and hence further developing the tumours.
• If the gene that oestrogen acts on is one that controls cell division and growth, then it will be activated and its continued division could produce a tumour. For example, oestrogen can cause proto-oncogenes of cells in breast tissue to develop into oncogenes, causing breast cancer.