Certain cells in the body, such as prostate and breast, have hormone receptors on their surface. Hormones that naturally circulate in the body bind to these receptors and stimulate the cell to grow. Some cancer cells have many more of these receptors than normal, in this situation, the hormone receptors are said to be “overexpressed.” These cells are particularly sensitive to the growth-stimulating effects of hormones. Hormone therapy either reduces the amount of hormone circulating in the body or blocks the receptors so that the hormones cannot bind and stimulate the cell. Thus, hormone therapy prevents some cancer cells from growing, but does not directly kill them.