Hormone treatment in breast cancer

In the fight against breast cancer, hormone therapy is one of the most important weapons in an oncologist’s arsenal. 

Hormone therapy is the use of medicines to block or suppress the hormones estrogen and progesterone, in order to prevent certain cancer cells from growing.

Approximately 60% of breast cancers have the estrogen (ER) and progesterone (PR) receptors present. This means that cancer growth is stimulated by the presence of these hormones in the blood.

Estrogen and progesterone are present in the blood of all women. In premenopausal women, these hormones are produced by the ovaries and, in post menopausal women, the hormones are produced by muscle and fat tissue.

When someone is diagnosed with breast cancer, one of the most important tests performed is to determine the presence, or absence, of the estrogen and progesterone receptors in the cancer. The presence of these receptors allows the doctor to use hormone blocking medications to control the cancer.

There are three main groups of medications used in the hormonal treatment of breast cancer:

Estrogen Receptor Blockers of which Tamoxifen is the most common. These drugs attach themselves to the estrogen receptor and prevent the circulating estrogen in the blood from stimulating the cancer.

Aromatase Inhibitors of which there are three, namely anastrozole, letrozole and exemestane.

These three drugs all prevent the body from producing estrogen in the muscles and fat cells. They have no effect on the estrogen produced in the ovaries.

GNRH Antagonists are given as an injection and stop the ovaries from producing estrogen.

Hormone blocking in ER positive cancer can take a number of different routes:

Firstly, the drugs are most commonly used in the adjuvant treatment of cancer. This means that the breast tumour will have been removed surgically and the patient will have received chemotherapy and/or radiation therapy to reduce the chances of the cancer returning. On completion of the chemotherapy and radiation therapy, the hormone tablets would then be prescribed by the oncologist for a period of five years as a further protection against the cancer returning.

Secondly, the hormone blockade  can be used in metastatic (stage 4) cancer after chemotherapy. Chemotherapy would be used to shrink the cancer and stop it from growing and spreading, but is unable to cure the cancer. The hormone blocking drugs would then be prescribed by the oncologist, to be taken indefinitely, in an attempt to slow down or prevent the cancer from growing.

Thirdly, hormone blocking drugs are used as primary therapy when a person is not well enough, or unable, for any reason to take chemotherapy.

These drugs are very successful in the treatment of cancer but work a lot slower than chemotherapy.

Unfortunately, as in most cases with medications, these drugs have side effects. The side effects are predominantly related to the reduction and prevention of estrogen and progesterone from performing their natural jobs in the body.

Very common side effects are hot flashes, dry skin and dry mucous membranes (particularly in the genital area), reduction in libido, depression and joint and muscle aches.

Less common side effects are fatigue, nausea and brittle nails and hair.

Very uncommon side effects, but a most important to watch for, are an increased risk of blood clots and endometrial cancer. Although very serious, these are not common. Your doctor will be very aware of these risks and monitor for them.

There is also a risk of osteoporosis and again your doctor will recommend regular bone density tests to check for this.

These side effects may seem very intimidating and scary, so it is important to discuss any fears or reservations you may have regarding this treatment with your doctor before deciding on treatment.

The benefits of the treatment far outway any risks or side effects and there are many ways that your doctor can assist with the side effects.

Written by Dr Owen Nosworthy