Breast cancers often use a woman’s own hormones in order to grow. Given this dependence, a powerful way to prevent a tumors growth is to block its access to these hormones. We can tell if a cancer is hormone dependent by measuring hormone receptors on the tumor cell surface. Your doctor will refer to these as “ER” and “PR” meaning “Estrogen Receptor” and “Progesterone Receptor.” When these are positive, use of estrogen blocking drugs, such as tamoxifen, or the aromatase inhibitors are important components of the overall treatment plan.
Tamoxifen has been used extensively in treating breast cancer with good long term follow up that proves its effectiveness. It is taken as a pill once daily for 5 years and it fundamentally changes the breast’s environment in a way that discourages the growth of cancer. This effect lasts long after a woman stops taking the drug. While it is generally well tolerated, it can cause hot flashes in some, and it is associated with a small risk of developing uterine cancer or blood clots.
Aromatase Inhibitors such as “Arimidex” and “Femara” work in a fundamentally different way than tamoxifen. They block the production of estrogen by fatty tissue throughout the body, including the breast itself. Estrogen is produced in these tissues using an enzyme called aromatase, and this becomes the most important source of estrogen after menopause. These drugs are only effective in women who are beyond menopause and are not used in women who still have active menstrual cycles.
The aromatase inhibitors haven’t been around as long as tamoxifen so we don’t have the same kind of long term follow up, but we do have strong evidence that they reduce the chance that the cancer will recur and they are better at preventing disease development in the opposite breast. These drugs do not carry the same risk of uterine cancer or blood clots as Tamoxifen does and they are quickly becoming the drug of choice for post menopausal women with hormone receptor positive breast cancer.
Hormonal therapies can be given in addition to chemotherapy, but in some cases, they can be used instead of chemotherapy. The stronger the hormone receptor status is, the more benefit the woman enjoys. Older women with strongly receptor positive disease are particularly good candidates for using hormonal treatment as their primary systemic therapy instead of chemotherapy. For most others, a combination of chemotherapy and hormonal therapy is optimal. A very useful website for estimating the relative benefits of hormonal therapy and chemotherapy after breast cancer surgery is available at AdjuvantOnline.com. This website was developed by Mayo Medical Clinic, and it uses a vast database of breast cancer patients and their outcomes in order to give both patients and physicians a realistic look at what each of these therapies have to offer in terms of preventing recurrence and improving survival.