Endocrine therapy

Endocrine therapy is a very effective treatment for breast cancers that are sensitive to hormones. Hormones act as chemical messengers in our body. Certain organs like ovaries produce hormones that reach various tissues and cells through the bloodstream to affect their function. They also play an important role in the start and development in about 80% (8 out of 10) breast cancer cases.

Ovaries produce oestrogen and progesterone (feminine hormones) in pre-menopause women. Other tissues, like fat and skin, produce the hormones oestrogen and progesterone in both post-menopause and pre-menopause women and men. Oestrogen promotes the development and maintenance of female sex characteristics and the growth of long bones. Progesterone plays a role in the menstrual cycle and pregnancy.

Oestrogen and progesterone also promote the growth of hormone-sensitive (or hormone-dependent) breast cancers. Hormone-sensitive breast cancer cells contain proteins called “hormone receptors” that become activated when hormones bind to them. If cancer cells contain oestrogen receptors they are called oestrogen positive cancer cell or for short ER+. If they do not contain oestrogen receptors, they are called oestrogen negative or ER-. Similarly, cancer cells may be progesterone positive (PR+ or sometimes PgR+) if they contain progesterone receptors, or progesterone receptors negative (PR- or PgR-) if they do not. About 80% of breast cancers contain both receptors or at least one of them.

How does hormone therapy work?

Cancer cells that contain hormone receptors (ER+ and/or PgR+) feed on oestrogen and progesterone. If we deprive these cells of oestrogen and progesterone we reduce their ability to divide and grow. This should reduce the rate of cancer recurrence in the future or reduce the rate of cancer growth and spread.

They are three mechanisms to deprive cancer cell of oestrogen and progesterone:

  1. Blocking ovarian function: Because the ovaries are the main source of oestrogen in premenopausal women, oestrogen levels in these women can be reduced by eliminating or suppressing ovarian function. This is done either surgically in an operation to remove the ovaries by treatment with drugs called gonadotropin-releasing hormone (GnRH) agonists. Zoladex is an example of ovarian suppression drugs
  2. Blocking oestrogen production: Drugs called aromatase inhibitors are used to block the activity of an enzyme called aromatase, which the body uses to make oestrogen in the ovaries and in other tissues. Aromatase inhibitors are used primarily in postmenopausal women because the ovaries in premenopausal women produce too much aromatase for the inhibitors to block effectively. However, these drugs can be used in premenopausal women if they are given together with a drug that suppresses ovarian function. Examples of aromatase inhibitors are anastrozole (Arimidex), letrozole (Femara) and exemestane (Aromasin).
  3. Blocking oestrogen’s effects: these drugs interfere with oestrogen’s ability to stimulate the growth of breast cancer cells. Examples are tamoxifen and fulvestrant (Faslodex), both of them are effective in pre- or post-menopausal women.

When are Hormones therapy used?

  • After breast cancer surgery to reduce the rate of cancer returning back in the future and enhance the rate of cure.
  • When breast cancer has already spread (stage 4) to achieve control and prevent further spread.
  • Occasionally, before surgery to reduce the size of breast cancer and prevent early spread of cancer to other parts of the body.

What are the side effects of Hormone Therapy:

This largely depends on the drug being used. Here you will find a link to an approved list of side effects for each of commonly used drugs:

Letrozole (Femara ®)

Anastrozole (Arimidex ®)

Exemestane (Aromasin ®)


Fulvestrant (Faslodex ®)