Hormone Therapy: The Basics
What are hormones and how are they used as therapy?
Hormones are chemicals that are made by the organs of the body's endocrine system (the pancreas, and the pituitary, thyroid, and adrenal glands). These chemicals move through the body in the bloodstream. They help each organ do its job. Hormones regulate almost every cell in the body. Some examples of hormones are estrogen, testosterone, insulin, thyroid hormone, cortisol, and epinephrine.
Some cancers need hormones in order to grow. Blocking the action of these hormones might stop the cancer from growing. There are a few ways this happens:
- Block the hormones from acting: Cells have "receptors" on their surface that certain hormones connect to and trigger activity inside the cells. By blocking the receptor, the hormone is not able to connect to its receptor.If the hormone's normal spot on the cell is already taken, the hormone cannot attach to and activate the cell.
- Prevent the body from making the hormone: This can be done with medication to block the production of the hormone, or with surgery to remove the organ that makes it. For example, removing the ovaries decreases the amount of estrogen being made.
- Remove the hormone receptors on cells or change their shape: The hormone then cannot attach itself to the cell receptor to activate it, making the hormone unable to work.
Hormone therapy that is used to treat certain cancers is not the same as hormone replacement therapy. Hormone therapy is used to block hormones or their actions. Hormone replacement therapy, which is not a cancer treatment, is when hormones are given to replace the ones the body no longer makes to treat menopause-related symptoms.
How is hormone therapy given?
Hormone therapy is most often used to treat breast and prostate cancers. Research is being done to see if hormonal therapy could be used to treat other cancer types. Hormone therapy can be given in a few ways:
- Oral medication – Taken by mouth.
- Injection – Given by an injection under the skin (subcutaneous) or in the muscle (intramuscular).
- Surgical intervention – Removal of the ovaries in women, or testicles in men, causes lower levels of hormones being made.
Hormone therapy is a "systemic" therapy, meaning that it travels throughout the body. Surgery and radiation therapy are "local" treatments.
What are the side effects of hormone therapy?
The side effects are caused by the lack of whatever hormone is being blocked or inactivated. For women, these effects are similar to those experienced with menopause, which is the body's natural decline in estrogen production with age. Side effects can include: hot flashes, night sweats, weight gain, vaginal dryness, and headache. Some side effects are caused by the hormone therapy. These can include: nausea, hair loss or thinning, muscle aches and joint pain, and, more seriously, blood clots and increased risk of uterine/endometrial cancer.
In men, the side effects can include hot flashes, tiredness, breast tenderness or enlargement, nausea, loss of sex drive, and impotence.
This decrease in the body's natural hormones can put men and women at higher risk for developing osteoporosis. Bisphosphonate therapy may be used to counteract this side effect. In addition, your healthcare provider may recommend taking steps to decrease the risk or severity of osteoporosis. This may include increasing calcium and vitamin D intake through diet or supplements, participating in weight-bearing exercise and avoiding tobacco and alcohol use (which increases osteoporosis risk). Learn more about bone health and cancer.
How do I know if hormone therapy is working for me?
This depends on the type of cancer being treated. Many patients will have imaging tests (CT scans, MRI scans, PET scans) to see how the tumor is responding (shrunk, stayed the same, or grown). Some types of tumors can be followed using a specific "tumor marker.” A tumor marker is either made directly by the tumor, or by the body in response to the tumor, and can be measured with a blood test. If the therapy is working, one would expect the tumor marker level to decrease. In some cases, a decrease in a patient's symptoms may be able to signal if the medications are shrinking the tumor or not. Talk with your healthcare provider about your tumor marker levels.
Classes of Hormone Therapy
An antiestrogen or estrogen blocker works by blocking estrogen receptors in breast tissue. While estrogen may not cause breast cancer, it is needed for the cancer to grow in some breast cancers. With estrogen blocked, the cancer cells that feed off estrogen may not be able to survive.
Estrogen receptor antagonist
Every person reacts differently to medications, so it is hard to predict what side effects each patient will have. However, the most common side effects in this category of medications include hot flashes, night sweats, weight gain, vaginal dryness and nausea. Blood clots and endometrial cancers are rare but can occur with these medications.
In women who have gone through menopause, estrogen is mainly made by converting androgens (sex hormones produced by the adrenal glands) into estrogens. An enzyme called aromatase makes this conversion happen. Aromatase inhibitors block this conversion, leading to less estrogen in the body.
Common side effects of these medications are hot flashes, night sweats, headache, nausea, hair thinning, vaginal dryness, muscle aches, and joint pain.
Other Hormone Treatments Used for Breast Cancer
Hormone-sensitive breast cancers can also be treated with other hormone agents.
Androgen, works by opposing the activity of estrogen
A form of progesterone, works by interfering with cell growth in ER+ cells.
LHRH agonist, works by stopping production of leutinizing hormone by the pituitary gland. LH causes the ovaries to make estrogen.
Most prostate cancers need testosterone to grow. Testosterone is an androgen made by the testes and adrenal glands. The production of testosterone can be stopped by surgically removing the testicles or through medication therapy. Anti-androgens work by blocking testosterone receptors, and preventing testosterone from attaching to these receptors found in the prostate cancer cells. Without testosterone, the cancer cells may either grow more slowly or stop growing altogether. You may hear this treatment called androgen deprivation therapy or ADT.
Every person reacts differently to medications, so it is hard to predict what side effects each patient will have. However, the common side effects for this category of medications include hot flashes, breast tenderness, nausea, loss of sex drive, and impotence.
There is also a second generation of these medications that block the androgen receptors more strongly and are more specific.
Luteinizing Hormone-Releasing Hormone Agonist (LHRH Agonist)
A hormone called luteinizing hormone, made by the pituitary gland, helps the testicles make testosterone. LHRH agonists stop the pituitary gland from making luteinizing hormone. This lessens the amount of testosterone in men. The cancer cells may then grow more slowly or stop growing. These are sometimes called gonadotropin-releasing hormone blockers (GnRH blockers). You may hear this treatment called androgen deprivation therapy or ADT.
Common side effects of these medications are tiredness, breast tenderness, nausea, loss of sex drive, and impotence.
If hormone therapy is part of your treatment plan, talk with your care team about which medications or surgeries may be right for you.
American Cancer Society. 2021. Hormone Therapy for Breast Cancer.
Mayo Clinic. 2020. Hormone Therapy for breast cancer.
National Cancer Institute. 2015. Hormone Therapy to Treat Cancer.
National Cancer Institute. 2021. Hormone Therapy for Prostate Cancer.