Hormone Therapy (Hormone-Blocking Therapy)

Hormone Therapy (Hormone-Blocking Therapy)

Hormone therapy is considered a systemic therapy in the treatment of breast cancer. Hormone therapy is recommended for patients whose tumors are positive for either the estrogen (ER) or progesterone (PR) receptors. In patients with hormone-positive tumors, these hormones, which are naturally made by the body, cause the cancer to grow. The goal of hormone therapy is to either block the production of hormones or to block the hormones from working.

Hormone blocking therapy is most often prescribed as an adjuvant therapy (after surgery) to decrease the risk of the cancer coming back, but can also be used in the neoadjuvant setting (prior to surgery) to decrease the size of the cancer in the breast. Hormone blocking therapy is also used to treat breast cancer that has recurred or spread. Most hormone blocking therapy drugs are taken daily in pill form.

Drugs That Block Hormones

Selective Estrogen Receptor Modulators (SERMs)

Tamoxifen is the most well known of the SERMs prescribed today.  It acts by blocking estrogen from attaching to the estrogen receptor on cancer cells. It is a “selective” modulator because on other cells, such as those in the uterus, it acts like estrogen, increasing the hormone effect on that organ. Raloxifene (Evista) and toremifene (Fareston) are other types of SERMs that may be prescribed by your doctor.

Most Common Side Effects of SERMs

  • Hot flashes
  • Vaginal dryness
  • Night sweats
  • Mood swings
  • Fatigue

More Serious Side Effects of SERMs

  • Blood clots (especially in women who smoke)
  • Uterine cancer (seen with Tamoxifen only)
  • Cataracts
  • Stroke

Estrogen Receptor Downregulators (ERDs)

Fulvestrant (Faslodex) is the only ERD currently prescribed for the treatment of breast cancer. Fulvestrant, which is given to patients who have gone through menopause,  works like a SERM in the breast tissue. Unlike other hormonal therapy drugs, fulvestrant is a liquid that is injected into a muscle monthly.

Most Common Side Effects of Fulvestrant

  • Pain at the injection site
  • Nausea/vomiting
  • Diarrhea or constipation
  • Sore throat
  • Back pain
  • Headaches
  • Hot flashes

Drugs That Lower Hormone Levels

Aromatase inhibitors (AIs) are medications that stop the body from making estrogen. These drugs are prescribed in pill form to women who have gone through menopause.

Most Common AIs

  • Anastrozole (Arimidex)
  • Exemestane (Aromasin)
  • Letrozole (Femara)

Most Common Side Effects of AIs

  • Joint pain
  • Hot flashes
  • Vaginal dryness
  • Night sweats
  • Osteoporosis

If your doctor prescribes an AI, it is very important that you undergo a bone density test. If your bone density is found to be low, you can be prescribed a medication that will help strengthen your bones while you are on the AI.

Ovarian Suppression

In premenopausal women, most of the estrogen in the body is produced by the ovaries. Ovarian suppression can be accomplished by surgery or with medications.


Oophorectomy is the surgical removal of the ovaries.  This puts a patient into menopause permanently. Because estrogen is made in small amounts elsewhere in the body, you may still be prescribed tamoxifen or an AI to block these hormones.

Ovarian Suppressive Medications

Medications to suppress the ovaries from making estrogen are also available. These medications temporarily shut down the hormone production of the ovaries, meaning that when the medication is stopped the ovaries will start to make hormones again.

The two most common ovarian suppressive medications are goserelin (Zoladex) and leuprolide (Lupron). They are both luteinizing hormone-releasing hormone (LHRH) agonists and work by telling the ovaries to stop making hormones. They are also given as injections, usually monthly.

Most Common Side Effects of Ovarian Suppressive Medications

  • Pain at the injection site
  • Hot flashes
  • Nausea
  • Weight gain
  • Bone pain