Breast Cancer Hormone Basics

What is "estrogen" and how is it related to breast cancer?

Oestrogen is a hormone that regulates a number of metabolic processes in a woman's body as well as a man's body, but there is more oestrogen circulating in women than there is in men. Oestrogen is important for breast development and breast health, but for a woman who is exposed to oestrogen for a long period of time over her lifetime, there can be a greater risk of developing breast cancer.

What is a "hormone receptor status test"?

A hormone receptor status test is an important test that is done on the breast cancer specimen itself. It's a test the pathologist does to determine whether there are oestrogen receptors or progesterone receptors on the cancer cells themselves. If there are, the cancer is likely sensitive to oestrogen and progesterone. It can be beneficial to block the oestrogen and block the progesterone if that's on the cancer, because if there are any cancer cells left behind, it can use those hormones to grow. So, in those individuals, tamoxifen and aromatase inhibitors may be beneficial medications to prevent breast cancer relapses, or if the cancer's already metastatic, to treat the cancer without requiring chemotherapy.

What is the relationship between hormone replacement therapy and breast cancer?

Hormone replacement therapy is a treatment with synthetic estrogens and progestins that sometimes women take after they've gone through menopause when their body is no longer producing it's own estrogen or it's own progesterone. Then, at times, physicians will prescribe these hormones, these medications for women to take. The problem is that we thought, many years ago, that there were a lot of benefits to hormone replacement therapy – that it reduced a woman's hot flashes, it decreased osteoporosis. We thought that it would also decrease cardiovascular disease, that it would decrease stroke, improve cognition and prevent Alzheimer's. But, as it turns out, when we did the large studies needed to determine these effects, that there was actually increased risk of heart attacks, increased risk of cardiovascular events, worsening of Alzheimer's, and we actually found it to increase the risk of breast cancer by about 3%. Now, there's some controversy as to whether it's the estrogen with the progestins that increases that risk – and whether the estrogen alone would not increase the risk of breast cancer. There's a lot of hesitancy for prescribing hormone replacement therapy today for women in the United States for women of post-menopausal symptoms because there are a number of potentially adverse side effects from them.