Treatment with Hormone Therapy
Some types of breast cancer are affected by hormones, like estrogen and progesterone. These are substances that function as chemical messengers in the body, affecting the actions of cells and tissues, often reaching their targets through the bloodstream. Some breast cancer cells rely on these hormones to fuel their growth. Hormone-sensitive breast cancer cells contain proteins called hormone receptors—estrogen receptors (ERs) and progesterone receptors (PRs)—that become activated when hormones bind to them. The activated receptors cause changes in the expression of specific genes, which can stimulate cell growth.
Hormone therapy (also called hormonal therapy, hormone treatment or endocrine therapy) can block or stop these hormones from attaching to these receptors and can reach cancer cells almost anywhere in the body, not just in the breast. It slows or stops the growth of hormone-sensitive tumors by blocking the body’s ability to produce hormones or by interfering with the effects of hormones on breast cancer cells. It's recommended for women with tumors that are hormone receptor-positive. It does not help women whose tumors don't have hormone receptors.
Types of Hormone Therapy
There are different types of hormone therapy for breast cancer. Most either lower estrogen levels or stop estrogen from acting on breast cancer cells. The choice of hormonal therapy depends on if a patient has gone through menopause.
- For premenopausal women, our medical oncologists may recommend an estrogen receptor blocker, such as tamoxifen.
- For postmenopausal women, our team may suggest an aromatase inhibitor, which blocks estrogen production, starving cancer cells of the hormones they need for growth.
Treatments That BLOCK Estrogen Levels
There are two main drugs that block estrogen.
- Tamoxifen
This drug blocks estrogen receptors on breast cancer cells. It stops estrogen from connecting to the cancer cells and telling them to grow and divide. While tamoxifen acts like an anti-estrogen in breast cells, it acts like an estrogen in other tissues, like the uterus and the bones. Because of this, it is called a selective estrogen receptor modulator (SERM).
In addition, tamoxifen can be used to help lower the risk of developing breast cancer in women who are at high risk.
Tamoxifen can also be used to treat women who have had breast-conserving surgery for ductal carcinoma in situ (DCIS) that is hormone receptor-positive. Taking tamoxifen for five years lowers the chance of the DCIS coming back. It also lowers the chance of getting an invasive breast cancer in both breasts.
For women with hormone receptor-positive invasive breast cancer treated with surgery, tamoxifen can help lower the chances of the cancer returning and increase life expectancy. It can also lower the risk of developing cancer in the other breast.
Tamoxifen can be started either after surgery (adjuvant therapy) or before surgery (neoadjuvant therapy) and is usually taken for five years but can be taken up to 10 years. For women with hormone-positive breast cancer that has spread to other parts of the body, tamoxifen can often help slow or stop the growth of the cancer and might even shrink some tumors.
Tamoxifen is taken once a day orally by pill.
- Fulvestrant (Faslodex)
Fulvestrant is a drug that blocks and damages estrogen receptors in post-menopausal women. It is known as a selective estrogen receptor degrader (SERD); it acts like an anti-estrogen throughout the body. Fulvestrant is given alone to treat advanced breast cancer that has not been treated with other hormone therapy. It can also treat advanced breast cancer after other hormone drugs have stopped working. It is given by injections into the buttocks. For the first month, the shots are given two weeks apart. After that, they are given once a month.
Treatments That LOWER Estrogen Levels
Some hormone treatments work by lowering estrogen levels. Aromatase inhibitors (AIs) are usually used for patients who have gone through menopause. Before menopause, most estrogen is made by the ovaries. But for women whose ovaries aren’t working, either due to menopause or certain treatments, a small amount of estrogen is still made in the fat tissue by an enzyme called aromatase. AIs work by blocking aromatase from making estrogen.
A Combination Approach
For women who have early-stage breast cancer and have not gone through menopause at diagnosis, our team may recommend taking tamoxifen first, and then taking an AI if they go through menopause during treatment. Another option is to take a drug called a luteinizing hormone-releasing hormone (LHRH) analog, which turns off the ovaries, along with an AI. An AI should not be taken alone for breast cancer treatment in pre-menopausal women because it is unsafe and can increase hormone levels.
Side Effects of Hormone Therapy
Because hormonal therapies can lead to a number of side effects, our care team will review them with each patient. The most common potential side effects include menstrual irregularities, infertility, hot flashes, decreased libido, night sweats and vaginal dryness.