ENDOCRINE THERAPY FOR BREAST CANCER

Endocrine therapy (also known as hormone therapy or hormone-blocking therapy) is used to treat breast cancers that are hormone receptor positive.

Around 70 to 80% of breast cancers are hormone receptor positive. These cancers have receptors for the female hormones oestrogen and/or progesterone on the inside of the cancer cells and are stimulated to grow by these hormones.

Endocrine therapy works by ‘starving’ cancer cells of oestrogen that make them grow. This lowers the risk of breast cancer returning or a new breast cancer developing in the treated breast or in the other breast.

Endocrine therapy may be recommended after other breast cancer treatments like surgery, chemotherapy or radiotherapy have been completed. Sometimes it is used to shrink breast cancer before surgery (neoadjuvant endocrine treatment).

There are several different types of endocrine therapy. The choice will depend on the type of breast cancer you have and whether you have reached menopause.

Tamoxifen works by stopping cancer cells from responding to oestrogen. It is taken as a tablet once a day for 5 to 10 years. Tamoxifen can be given to premenopausal and postmenopausal women and men.

Common

• Hot flushes and sweats
• Irregular vaginal bleeding in premenopausal women
• Vaginal irritation, dryness or discharge
• Fluid retention and weight gain

Uncommon

• Light-headedness, dizziness, headache
• Fatigue
• Rash
• Nausea
• Depression or mood swings

Rare

• Blood clots in the veins in the legs or lungs
• Cancer of the endometrium
• Eye problems
• Hair thinning
• Changes to the liver
• Changes in memory and thinking

Aromatase inhibitors reduce the amount of oestrogen made by the body. They are recommended only for postmenopausal women. The 3 aromatase inhibitors are anastrozole (Arimidex), exemestane (Aromasin) and letrozole (Femara). They are taken daily as a tablet, usually for 5 to 10 years.

Common

• Muscle aches and pains
• Hot flushes
• Vaginal dryness

Uncommon

• Reduced sex drive
• Osteoporosis
• Difficulty sleeping
• Fatigue 

For premenopausal women, there are treatments that can stop the ovaries from producing oestrogen either temporarily or permanently. These are sometimes recommended in addition to tamoxifen.

The ovaries can be shut down temporarily with medication, usually with a course of monthly injections of goserelin (Zoladex). This gradually causes the levels of oestrogen to fall, which leads to temporary menopause. Side effects are similar to symptoms of permanent menopause and come on gradually over weeks or months.

Surgical removal of the ovaries, known as oophorectomy, is a permanent way to reduce the levels of oestrogen. This can also reduce the risk of ovarian cancer. Oophorectomy is usually done with a keyhole technique under general anaesthesia as day surgery. Symptoms of menopause may start suddenly in the few days following surgery.

Hormone Therapy & Breast Cancer by Breast Cancer Network Australia

Hormonal Therapies For Breast Cancer by Westmead Breast Cancer Institute