There are two main types of hormonal drugs for invasive breast cancer. One type is the selective estrogen receptor modulators (SERMs), and the other is the aromatase inhibitors.
Tamoxifen is the most common SERM used in the treatment of breast cancer. Aromatase inhibitors are hormonal therapy used only in postmenopausal women. Side effects can be managed by working with your medical team.
You may be offered several types of treatment for breast cancer, such as surgery, radiation therapy, chemotherapy, targeted therapy, and hormonal therapy. This article will focus on hormonal therapy for breast cancer.
What is Invasive Cancer?
Before we talk about hormonal drugs used to treat invasive breast cancer, let’s define some terms to help you understand what invasive breast cancer is.
- Invasive cancer means the cancer has spread outside the layer of tissue where it initially started – the cancer is growing into the surrounding, healthy tissue of the same part of the body. You may also hear it described as infiltrating cancer.
- Non-invasive cancer is the opposite – the cancer has not invaded into the normal breast tissue.
- Non-metastatic cancer is cancer that has not spread to other parts of the body – the cancer is in the primary site of the body where it started. Non-metastatic cancer is often referred to as early stage breast cancer.
- Metastatic cancer is cancer that has spread to other parts of the body, such as the bones, lung, or liver.
Hormones and Hormone Receptors in Breast Cancer
Some types of cancers, like breast cancer, grow in part in response to certain hormones. Hormonal therapy is a cancer treatment that uses medications to slow or stop cancer growth by changing either the ability of your own hormones to connect with and block cancer cells from receiving estrogen or by decreasing estrogen levels in your body.
The hormone receptors on the breast cancer reflect the cancer cell’s own biology. That is, whether or not the tumor has hormone receptors is not related to your own estrogen levels.
Hormonal therapy is also called endocrine therapy because hormones are made by your body’s endocrine system.
The two main hormones that affect breast cancer are estrogen and progesterone. Estrogen and progesterone are made in the ovaries of women and in the adrenal glands of men and women. Estrogen plays a role in breast development, and progesterone plays a role in menstrual cycle and pregnancy.
A receptor is a protein found inside or on the surface of a cell. Hormones bind to hormone receptors on cells throughout your body. Breast cancer cells have an estrogen receptor, a progesterone receptor, both, or neither. Estrogen and progesterone attach to cancer cells that have estrogen and progesterone receptors. When the hormones attach to the cancer cells, they aid cancer cell growth. This is why hormonal therapy as cancer treatment focuses on estrogen and progesterone.
Some breast cancer cells have hormone receptors specifically for estrogen or progesterone.
- The secreting cell is the cell that makes the hormone, such as the ovaries, adrenal glands, and testes.
- The blue dot is the hormone that is made in the cell, such as estrogen or progesterone.
- The target cell is a breast cancer cell.
- The green block on top of the target cell is the hormone receptor where the estrogen or progesterone binds.
Hormone receptor-positive (HR+) breast cancer cells have estrogen hormone receptors, progesterone hormone receptors, or both. Most breast cancer cells are HR+.
Estrogen receptor-positive (ER+) cells are cells that appear to respond to estrogen and may stop growing or die when estrogen is blocked from cancer treatment.
Progesterone receptor-positive (PR+) cells are cells that appear to respond to progesterone to grow and may stop growing or die when progesterone is blocked from cancer treatment.
Cancer cells can have both types of hormone receptors.
Some cancer cells have neither hormone receptor in which case they are referred to as “hormone receptor-negative” (HR-negative). If breast cancer cells do not have the estrogen or progesterone receptors, they are called estrogen receptor-negative (ER-) or progesterone receptor-negative (PR-).
- ER- cells do not need estrogen to grow and will continue to grow even if treatment is used to block estrogen.
- PR- cells do not need progesterone to grow and will continue to grow even if treatment is used to block progesterone.
Hormonal Drugs for Invasive Breast Cancer
There are two major types of hormonal therapy for invasive breast cancer, the selective estrogen receptor modulators (SERMs) and aromatase inhibitors.
SERMs copy the effects of estrogen in some parts of your body but block the effects of estrogen in other parts of your body. In breast tissue, SERMs block the effects of estrogen, thereby preventing the ER+ cancer cells from growing. Examples of SERMs are listed below:
- tamoxifen (Nolvadex)
- raloxifene (Evista)
- toremifene (Fareston)
- fulvestrant (Faslodex) (this medication is actually a “disruptor” of the estrogen receptor)
The most commonly used SERM is tamoxifen. Some side effects include hot flashes, night sweats, leg cramps, and vaginal dryness.
Other effects include a risk of bood clots, uterine (endometrial) cancer, vaginal bleeding, and high blood pressure. These are much less common than the side effects above.
Tell your doctor if you are experiencing any side effects from medications.
SERMs also decrease the risk of bone thinning (osteoporosis) in postmenopausal women and may decrease the risk of heart disease, especially when compared to the aromatase inhibitors.
Aromatase inhibitors stop the formation of estrogen in your body by tissues other than the ovaries. This prevents the ER+ cancer cells from growing because the estrogen that they use won’t be formed.
There are three aromatase inhibitors:
- Anastrozole (Arimidex)
- Letrozole (Femara)
- Exemestane (Aromasin)
Side effects include joint pain, bone pain, and menopausal symptoms such as vaginal dryness, and hot flashes.
Tell your doctor if you are experiencing any side effects.
The aromatase inhibitors increase the risk of osteoporosis and have a higher risk of heart side effects than SERMs.
Which Medication Will You Get?
These hormonal therapies are used for people with invasive breast cancer who are ER+. This means that their breast cancer has estrogen receptors, so they grow when estrogen binds to it. The treatment options are either a SERM or an aromatase inhibitor. The most commonly used SERM is tamoxifen. The choice of which medication your doctor chooses depends on a handful of reasons, two of which are whether you’ve finished menopause and your sex.
Women Before Menopause
If you are a woman who has not reached menopause yet, meaning you still experience your monthly period or blood work shows that your ovaries are still working, your first medication treatment will likely be the tamoxifen. The aromatase inhibitors do not work in people who have ovarian function.
Tamoxifen is also preferred as the first form of hormonal therapy in men with invasive breast cancer. The testes make both estrogen and testosterone. Testosterone is also converted to estrogen in your body. For men, tamoxifen is used to block the estrogen receptors in breast cancer cells to prevent naturally-made estrogen from binding to it. See the section below titled Men With Invasive Breast Cancer for more information about treatment for men with breast cancer.
Women After Menopause
If you have finished menopause or if you reached menopause after starting SERM treatment, then your doctor may start with or change to an aromatase inhibitor. Aromatase inhibitors stop the conversion of androgens (male sex hormones) to estrogen. This medication is used in people who have reached menopause because the estrogen in their body is no longer made in the ovaries.
Contraception and Fertility
Hormonal therapy can cause serious birth defects. It is important to use a contraceptive to avoid getting pregnant during treatment.
As written above, most breast cancer cells have the estrogen and progesterone receptors. Birth control pills and other hormonal birth control have similar hormones in them (estrogen and progesterone) because they are used to copy your body’s natural menstrual cycle.
We recommend that people with breast cancer not use hormonal forms of contraception. Below are examples of hormonal birth control options that should be avoided in people with breast cancer:
- Birth control pills
- Birth control patches
- Estrogen rings
- Estrogen implants
- Progesterone IUDs
Speak with your medical team about your options for birth control before starting treatment.
For people with invasive breast cancer, condoms are a good option. Copper IUDs and diaphragms with spermicide can be used as well because they do not have hormones in them.
If you have invasive breast cancer and you are still having periods, then the option of having children after your treatment is completed should be explored. Before you start your treatment for invasive breast cancer, ask your doctor and a fertility specialist about your options for having children.
Men With Invasive Breast Cancer
Although breast cancer mostly occurs in women, 1 out of every 100 breast cancers is in men. As explained earlier, testosterone is converted to estrogen in the body, so hormonal therapy is used for men as well. Men can receive either tamoxifen or an aromatase inhibitor.
There are two types of hormonal drugs for invasive breast cancer: SERMs and aromatase inhibitors. Menopausal state and sex are two of the main factors that determine which medication you get. You may be on one of these medications for about 5 to 10 years. If you have side effects, work with your medical team so that you can stay on hormonal therapy.
If you are still getting your monthly period before treatment, speak with your medical team about options for birth control and having children.
- National Cancer Institute Dictionary of Cancer Terms. cancer.gov. https://www.cancer.gov/publications/dictionaries/cancer-terms. Published February 2, 2011. Accessed July 20, 2020.
- Gradishar WJ, Anderson BO, Abraham J, et al. National Comprehensive Cancer Network Guidelines Breast Cancer. Version 5.2020 From the National Comprehensive Cancer Network; July 2020. https://www.nccn.org/professionals/physician_gls/pdf/breast.pdf. Accessed July 20, 2020.
- National Comprehensive Cancer Network (US). NCCN Guidelines for Patients: Breast Cancer – Invasive. Version 2020. Fort Washington, PA: NCCN; 2020.