How Do You Reduce Estrogen After Breast Cancer? Hormone Therapy

Breast cancer is categorized into two types based on what type of proteins are responsible for breast cancer, human epidermal growth factor receptor 2 (HER2):

• HER2-positive breast cancer
• HER2-negative breast cancer or hormone-receptive breast cancer (estrogen-receptive or progesterone receptive cancer)

The HER2 protein is a receptor found on the surface of breast cells that is involved in the normal growth of breast cells. When there is a defect in the HER2 gene that controls the production of HER2, it makes more than the required copies of HER2. Excess of HER2 results in breast cell overgrowth, which can lead to HER2-positive cancer.

When a person has been diagnosed with breast cancer, doctors check if they have HER2-positive breast cancer or hormone-receptive breast cancer. Diagnosis is made based on tests that check for the presence of HER2 protein in the breast tissue. 

Positive test results indicate HER2-positive cancer, while negative test results indicate hormone-receptive breast cancer, which may be either estrogen-positive or progesterone-positive cancer. Out of all breast cancer cases, 80% are estrogen-positive.

Detecting the type of breast cancer is essential to determining treatment: treatments targeted at HER2 protein, estrogen, or progesterone.

Of the five types of hormone therapy, the two most common are:

• Drugs that block estrogen receptors
• Treatments that lower estrogen levels

Three other types of hormone treatments that are rarely used now include:

• Megestrol acetate (Megace), a progesterone-like drug
• Androgens (male hormones)
• High doses of estrogen

Aromatase inhibitors (AIs) lower estrogen levels by stopping estrogen production. They work by blocking the aromatase enzyme. The aromatase enzyme helps produce estrogen in the fat tissue of postmenopausal women or women whose estrogen production has stopped due to treatments. Apart from use in postmenopausal women, these drugs can be used in premenopausal women in combination with another treatment, ovarian suppression.

Taken in the form of daily oral pills, the AIs used in the treatment of breast cancer include:

• Letrozole
• Anastrozole
• Exemestane

Aromatase inhibitors cause fewer side effects than tamoxifen and unlike tamoxifen do not cause uterine cancers. Chances of developing blood clots are also low. 

Possible side effects include:

• Muscle pain
• Joint stiffness and pain
• Osteoporosis (thin, brittle bones)
• Increased risk of fracture

If you have been put on AI, your bone density may be tested. Your doctor may prescribe drugs such as zoledronic acid or denosumab to strengthen and improve bone density.

Because the ovaries produce the majority of estrogen in premenopausal women, removing them or blocking them is one way to lower estrogen levels in breast cancer:

• Oophorectomy: Oophorectomy involves surgical removal of the ovaries.
• Luteinizing hormone-releasing hormone (LHRH) analogs: These block the signals that stimulate estrogen production in the ovaries. Common LHRH drugs include goserelin and leuprolide.
• Chemotherapy medications: Some chemotherapy medications damage the ovaries temporarily or permanently so that the ovaries stop producing estrogen.