Hormone Therapy for Breast Cancer

If you have received a diagnosis of hormone-receptor-positive breast cancer, it is important to know that hormone therapy (usually a pill that you take once a day) may be a viable treatment option for you. While it may seem less intimidating than other methods of treatment, you may still have concerns about its potential side effects. It is crucial to understand the details of hormone-blocking therapy and how it can benefit you. By gaining knowledge about this treatment option, you can face any potential side effects with confidence.

Hormone-blocking therapy, or endocrine therapy, is a type of cancer treatment used for certain types of breast cancer, specifically hormone receptor-positive breast cancer. There are proteins located on the surface of cells, known as hormone receptors, that play a crucial role in regulating the growth of normal and healthy breast cells. These receptors bind to hormones like estrogen and progesterone in the bloodstream, enabling breast cells to grow and function properly. In hormone receptor-positive breast cancer, hormone receptors are overproduced, leading to increased ability of cancer cells to use estrogen and progesterone to grow and divide and the resulting abnormal excessive growth of cancer cells. The presence of these over-expressed hormone receptors determines the hormone receptor status of breast cancer. Hormone receptor statuses are as follows:

• Estrogen receptor-positive only (ER+, PR-)

This type of cancer cell only has estrogen receptors.

• Progesterone receptor-positive only (ER-, PR+)

This type of cancer cell only has progesterone receptors. It is treated as hormone-receptor negative cancer. Progesterone receptor status is not used to make treatment decisions.

• Both estrogen receptor-positive and progesterone receptor-positive (ER+, PR+)

This type of cancer cell has both estrogen and progesterone receptors.

• Hormone receptor-negative or estrogen receptor-negative and progesterone receptor-negative (ER-, PR-)

This type of cancer cell has neither estrogen nor progesterone receptors, but may have other protein receptors, such as the HER2/neu receptor, that guide treatment decisions.

Cancer cells with a positive estrogen receptor type are classified as hormone receptor-positive. In general, hormone blocking therapy works by either reducing estrogen and progesterone production or preventing these hormones from binding to the hormone receptors on cancer cells to slow down or stop cancer growth. For this reason, hormone blocking therapy is only helpful for hormone receptor-positive breast cancer and is not normally used for hormone receptor-negative breast cancer. Endocrine therapy may be used alone or subsequent to other breast cancer treatment methods, such as surgery and radiation therapy.

There are several types of hormone blocking treatment. Some endocrine therapy drugs block estrogen receptors, while others lower estrogen levels.

Selective estrogen receptor modulators (SERMs)

SERMs prevent estrogen from binding to estrogen receptors on breast cancer cells. They attach themselves to these receptors so estrogen cannot attach to these proteins on the surface of breast cancer cells, preventing cancer cells from multiplying and growing. While they have anti-estrogen effects on breast cells, they act like estrogen in other tissues, such as the uterus and bones. As such, some SERMs, such as Tamoxifen, are normally recommended for hormone receptor-positive breast cancer patients who are premenopausal. Common SERMs include:

• Tamoxifen (taken as pills)
• Raloxifene (taken as pills)

Selective estrogen receptor degraders (SERDs)

SERDs work by attaching to estrogen receptors on breast cancer cells, like SERMs, but bind to them more tightly, causing them to break down. SERDs are used in the treatment of metastatic breast cancer only. These drugs have anti-estrogen effects throughout the body. Common SERDs include:

• Fulvestrant (taken as injections)
• Elascestrant (taken as pills)

Aromatase inhibitors (AIs)

AIs function by decreasing the estrogen production by body tissues other than the ovaries, for example the fat tissue. Aromatase, an enzyme found in various body organs, such as the breasts, is responsible for converting other hormones into estrogen. AIs hinder aromatase's ability to change other hormones into estrogen, decreasing the body's estrogen levels. In women, the ovaries produce most of the estrogen before menopause. After menopause, the ovaries stop producing estrogen, and aromatase is the primary source of estrogen production. As a result, AIs are usually recommended for postmenopausal women to prevent and treat certain breast cancer types. In pre-menopausal women, AIs can also be given together with a drug to prevent ovary production of estrogen called leuprolide. Common AIs include:

• Letrozole (taken as pills)
• Anastrozole (taken as pills)
• Exemestane (taken as pills)

As with all drug-related therapy, hormone therapy drugs have some potential side effects.

Regarding the treatment of breast cancer, hormone blocking therapy presents a less complex alternative in comparison to chemotherapy and radiation therapy. Consequently, you will not need to make frequent visits to the hospital, which can be a relief. Nevertheless, it is crucial to bear in mind that there are still potential side effects that may arise, which could cause some apprehension. In case you encounter any new side effects, it is highly recommended to inform your healthcare team, who will be able to provide you with the necessary guidance and support.