An Introduction to Hormone Therapy
Hormone therapy, also known as endocrine therapy, is a type of systemic cancer treatment that works by interfering with the body’s hormones. Certain cancers rely on specific hormones to grow and spread. Hormone therapy is designed to slow or stop the growth of these “hormone-sensitive” or “hormone-receptor-positive” cancers by cutting off their hormonal fuel supply.
It is a highly effective and foundational treatment for several common types of cancer, most notably breast cancer and prostate cancer. Unlike traditional chemotherapy, which attacks all fast-growing cells, hormone therapy is more targeted in its action, which generally results in a different set of side effects. The decision to use hormone therapy is based entirely on the specific characteristics of the cancer cells, which are determined by testing a sample of the tumor tissue in a laboratory.
The Principle: How Do Hormones Fuel Cancer?
Hormones are chemical messengers produced by glands in the body that travel through the bloodstream and regulate the function of various organs and tissues. Some tissues in the body, such as the breast and the prostate, have cells with “receptors”—proteins that act like docking stations for specific hormones. When a hormone binds to its receptor, it signals the cell to grow and divide.
In some types of cancer, the cancer cells retain these hormone receptors. This means that the body’s natural hormones can inadvertently fuel the cancer’s growth. For example:
- Many breast cancers are fueled by the female hormones estrogen and/or progesterone.
- Most prostate cancers are fueled by male hormones called androgens, the most well-known of which is testosterone.
Hormone therapy works by disrupting this process in one of two main ways: by stopping the body from producing the cancer-fueling hormone, or by blocking the hormone from binding to the receptors on the cancer cells.
The Role of Biomarker Testing
Before hormone therapy can be considered, doctors must determine if the cancer is hormone-sensitive. This is done by a pathologist who tests a sample of the tumor tissue (from a biopsy or surgery) for the presence of hormone receptors. This is a critical form of biomarker testing.
- For breast cancer, the tissue is tested for Estrogen Receptors (ER) and Progesterone Receptors (PR). If a cancer has a significant number of these receptors, it is called ER-positive and/or PR-positive.
- For prostate cancer, the cells are known to be driven by androgens, so specific receptor testing is less a part of the initial diagnosis but is fundamental to the understanding of the disease.
If a cancer does not have these receptors (e.g., an ER-negative breast cancer), it is “hormone-receptor-negative,” and hormone therapy will not be an effective treatment.
Hormone Therapy for Breast Cancer
For patients with ER-positive breast cancer, hormone therapy is a cornerstone of treatment. It is most often used as an adjuvant therapy after surgery and chemotherapy to reduce the risk of the cancer returning. The type of hormone therapy recommended often depends on whether the patient has gone through menopause.
- Blocking Estrogen Receptors: Drugs called Selective Estrogen Receptor Modulators (SERMs) work by sitting in the estrogen receptors on the cancer cells. This blocks the body’s natural estrogen from binding to the receptors, thereby preventing the cancer cells from being signaled to grow.
- Lowering Estrogen Levels: For postmenopausal women, the main source of estrogen is no longer the ovaries but the conversion of androgens into estrogen in fat tissue by an enzyme called aromatase. Drugs called Aromatase Inhibitors (AIs) work by blocking this enzyme, which drastically lowers the amount of estrogen in the body, starving the cancer cells of their fuel.
- Suppressing Ovarian Function: For premenopausal women, the ovaries are the main source of estrogen. In some situations, treatments can be used to temporarily or permanently stop the ovaries from producing estrogen. This can be done with monthly injections of drugs that shut down the ovaries, or through the surgical removal of the ovaries (oophorectomy).
Hormone Therapy for Prostate Cancer
Prostate cancer cells are dependent on androgens (male hormones) for their growth. Hormone therapy for prostate cancer is therefore focused on reducing the amount of androgens in the body or preventing them from reaching the cancer cells. This is known as Androgen Deprivation Therapy (ADT). ADT is the foundation of treatment for advanced or metastatic prostate cancer and is also used in combination with radiation therapy for some earlier stages of the disease.
- Lowering Testosterone Production: Most of the body’s testosterone is made in the testicles. The production is controlled by a hormone from the pituitary gland called Luteinizing Hormone-Releasing Hormone (LHRH). Drugs called LHRH agonists or LHRH antagonists are given as injections to stop the testicles from producing testosterone. This is a form of “medical castration.”
- Surgical Removal of the Testicles (Orchiectomy): This is a surgical procedure to remove the testicles, which permanently stops their production of testosterone. While less common today, it is a simple and effective method of ADT.
- Blocking Androgen Receptors: Other drugs, called anti-androgens, work by blocking the androgen receptors on the prostate cancer cells, preventing testosterone from binding to them.
How is Hormone Therapy Administered?
Hormone therapy can be delivered in several different ways, depending on the specific drug and the type of cancer being treated.
- Oral Medications: Many hormone therapies are pills taken daily at home. This is common for breast cancer treatments like SERMs and AIs.
- Injections: Several key hormone therapies, particularly for prostate cancer (LHRH agonists/antagonists), are given as injections. These may be administered in a doctor’s office on a schedule of once every one, three, or six months.
- Surgical Procedures: As mentioned, the surgical removal of hormone-producing organs—the ovaries (oophorectomy) for breast cancer or the testicles (orchiectomy) for prostate cancer—is a permanent form of hormone therapy.
Common Side Effects of Hormone Therapy
Because hormone therapy interferes with the body’s natural hormones, its side effects are related to this hormonal deprivation. The side effects differ between men and women and between different types of therapy.
Common side effects for women on hormone therapy for breast cancer may include:
- Hot flashes and night sweats
- Vaginal dryness or irritation
- Fatigue
- Joint and muscle pain (particularly with Aromatase Inhibitors)
- An increased risk of osteoporosis (bone thinning)
Common side effects for men on ADT for prostate cancer may include:
- Hot flashes
- Loss of libido and erectile dysfunction
- Fatigue and loss of muscle mass
- Weight gain
- An increased risk of osteoporosis and bone fractures
The medical team works closely with patients to monitor for and manage these side effects throughout the course of treatment.
Frequently Asked Questions
1. Is hormone therapy a form of chemotherapy?
No. This is a common point of confusion, but they are very different treatments. Chemotherapy uses powerful cytotoxic drugs to kill rapidly dividing cells throughout the body. Hormone therapy is a more targeted treatment that works specifically by blocking or lowering the amount of certain hormones that a cancer needs to grow. Their mechanisms of action and side effect profiles are very different.
2. How long do I need to take hormone therapy?
The duration of hormone therapy can vary greatly. For advanced or metastatic cancer, it is often continued for as long as it remains effective. In the adjuvant setting (after surgery to prevent recurrence), it is a long-term treatment. For example, women with breast cancer often take daily hormone therapy pills for five to ten years. Men receiving ADT for prostate cancer may be on it for several years or indefinitely.
3. Will hormone therapy work for my type of cancer?
Hormone therapy only works for cancers that are “hormone-receptor-positive,” meaning the cancer cells have receptors that are fueled by specific hormones. The most common examples are ER-positive breast cancer and androgen-sensitive prostate cancer. It is not an effective treatment for cancers that lack these receptors.
4. How does my doctor know if my cancer is hormone-sensitive?
This is determined by a pathologist who performs biomarker tests on a sample of the tumor tissue obtained from a biopsy or surgery. For breast cancer, the tissue is tested for the presence of estrogen receptors (ER) and progesterone receptors (PR). If these are present, the cancer is hormone-sensitive.
5. What are some of the most common side effects of hormone therapy?
The side effects are a direct result of depriving the body of certain hormones. The most common side effects are often similar to the symptoms of menopause, such as hot flashes, night sweats, and fatigue. For men on ADT, this can also include loss of libido. Long-term use can also increase the risk of bone thinning (osteoporosis).
6. Can hormone therapy be used as the only treatment for cancer?
In some situations, yes. For men with advanced prostate cancer, hormone therapy (ADT) is often the primary and sole treatment for long periods. However, it is more commonly used as part of a multi-modal treatment plan. For early-stage breast cancer, for example, it is a crucial adjuvant therapy used after surgery, radiation, and/or chemotherapy have been completed.
7. How is hormone therapy for breast cancer different from hormone therapy for prostate cancer?
They both work on the same principle—cutting off the hormonal fuel supply—but they target different hormones. Hormone therapy for breast cancer focuses on blocking the effects of the female hormone estrogen. Hormone therapy for prostate cancer focuses on blocking the effects of male hormones, known as androgens (like testosterone).
