Estrogen travels through the blood, but only the cells in estrogen target tissues, like the breast and uterus, can recognize and use estrogen because they have estrogen receptors . The estrogen and the estrogen receptor bind to form a unit that enters the nucleus of the cell. These specialized genes instruct the cell to make proteins that signal the cell to carry out important activities. Some of these signaling proteins can tell the cell to divide. Some forms of estrogen are stronger than others.
Stronger forms are more likely to initiate cell division than weaker forms.
In addition, some forms of estrogen stay in the body longer than others. One characteristic of a cancer cell is that it multiplies out of control. The progression from a normal cell to a cancer cell is a multistep process that includes the build-up of damage to the DNA in key genes that control cell division. Damage to a gene in DNA is called a mutation . This damage may happen in several different ways.