Hormones are produced by organs or cells in your body. Hormones, such as estrogen, affect bodily processes. Normal breast cells have receptors for estrogen and progesterone. Some, but not all, breast cancer tumors also have these receptors and need these hormones to grow. Such tumors are called estrogen and/or progesterone receptor positive, or hormone receptor positive. Breast cancer tumors are estrogen and/or progesterone receptor positive in approximately 60% of postmenopausal women. Lab tests of your cancer biopsy give your medical team this information. Receptors are very small parts of a cell. If estrogen is present, it will attach to an estrogen receptor and may make the tumor grow larger.
Estrogen does not cause breast cancer, though it may promote the growth of tumors. Here's how certain breast cancer cells live and grow with the help of estrogen: