Homones are a natural part of the body's chemistry. Some breast cancers are stimulated by the female hormones oestrogen and progesterone.
We treat these cancers by stopping these hormones from being released or blocking the cancer cell from feeding on them.
In New Zealand approximately 70% of breast cancers diagnosed are hormone receptor positive. This can mean that the cancer is being fed by the body’s production of oestrogen or progesterone or both. Hormone sensitive cells are said to be oestrogen positive (er+) or progesterone positive (pr+) or both.
For a summary of breast cancer treatment drugs, download this leaflet.
Tamoxifen is the most commonly used hormone-blocking drug. It is also called an “anti-oestrogen” drug because it works by attaching to the hormone receptors on cancer cells so that oestrogen cannot feed them. Some studies show that Tamoxifen can also stop cancer cells from dividing.
If you are prescribed Tamoxifen, you will be advised to take it orally on a daily basis for 5 or more years but its effects have been known to last beyond this period. Tamoxifen belongs to a class of drugs called selected oestrogen receptor modulators or SERMS.
Most people tolerate Tamoxifen with few or no side effects. You may experience hot flushes, vaginal dryness, or vaginal discharge when taking this drug. You may also experience mild nausea, decreased libido, fatigue, or depression. Some people are concerned about weight gain. It is important to adopt a healthy diet and try to exercise regularly. There is also an increased risk of developing a blood clot in the lungs or in the major veins of the legs, but this is rare. About 1% of women taking Tamoxifen for some years may develop uterine cancer, so any vaginal bleeding should be thoroughly investigated.
Download our tamoxifen patient information sheet.
Aromatase inhibitors are a newer class of drugs used to treat breast cancers that rely on oestrogen for growth. They work by blocking the production of oestrogen. Aromatase inhibitors are only suitable for postmenopausal women. They are not effective in pre-menopausal women who are still producing oestrogen from their ovaries. These drugs may also be prescribed for women who do not respond well to Tamoxifen or whose breast cancer becomes resistant to Tamoxifen.
Aromatase inhibitors include Anastrozole ( Arimidex)Letrozole (Femara), and Exemestane (Aromasin). All are currently funded in New Zealand for early breast cancer. They are all taken orally in pill form.
Common side effects of aromatase inhibitors include hot flushes, osteoporosis (weakening of the bones), muscular and joint aches and pains.
Recent research shows the addition of Anastrazole (Arimidex) to Tamoxifen (after 2-3 or 5 years) further reduces the risk of breast cancer recurrence (at 5 years, a 50% risk reduction with Tamoxifen, a further 26% risk reduction with the addition of Anastrozole).
Download our aromatase inhibitor patient information sheet.
Watch our webinar on learning to love Tamoxifen and AIs.
Oestrogen Receptor Downregulators (ERDs)
There is also a new type of hormone treatment called Oestrogen Receptor Downregulators (ERDs) becoming available. ERDs attach to the oestrogen receptors on cancer cells and block them, but they also cause the receptors to break down and stop functioning. With fewer receptors available, growth of cancer cells is slowed. The only ERD currently approved is Fulvestrant (Faslodex) and it is only approved for postmenopausal women with metastatic breast cancer that does not respond to other hormonal therapy such as Tamoxifen.
If you are taking Fulvestrant, you may experience mild nausea, vomiting, diarrhoea, headache and hot flushes. The drug is taken once a month by injection. This treatment is quite well tolerated by most women.
Ovarian block or Oophorectomy
The most effective way to reduce hormone production in premenopausal women is to stop production of oestrogen by removing or blocking the ovaries. This can be done by surgery, radiotherapy or medication.
Surgical removal of Ovaries – Oophorectomy
This is important if the breast cancer tumour is fed by oestrogen. Removing the ovaries reduces the level of oestrogen being produced by the woman. This operation can be performed laproscopically reducing scarring and hastening recovery.
Zoladex is an injected drug which reduces oestrogen production by switching off the message from the brain to the ovaries. Zoladex shuts off production of the hormone oestrogen by the ovaries. This can help reduce the growth of hormone sensitive cancers. It is used in both advanced and early pre-menopausal breast cancers with hormone sensitive disease.
Women may experience a return of their menstrual cycle after stopping the treatment. This is not guaranteed.
Megestrol Acetate (Megace)
An anti hormonal treatment used only for advanced or metastatic disease. It is a high dose progesterone tablet and may be used if Tamoxifen and Arimidex are not suitable. This works by counteracting the effect of natural oestrogen. The way this works is not entirely known. One of the major side effects of this treatment is increased appetite and weight gain.