Hormone Therapy in Early Breast Cancer

Hormone therapy, also called endocrine therapy, is medicine used to treat forms of breast cancer which grow in response to hormones. It involves taking medications or using other treatments to lower hormone levels and prevent the growth of cancer cells in the body.

What is hormone therapy?

Medicine used to treat forms of breast cancer that grow in response to hormones – oestrogen (ER) and/or progesterone (PR) receptor positive breast cancer – is called hormone or endocrine therapy.

Endocrine therapy involves taking a tablet once every day to prevent the body from making oestrogen and progesterone, or to stop hormones from stimulating the growth of cancer cells. For premenopausal women, further medications in the form of monthly injections may also be recommended to stop the ovaries from making oestrogen. Alternatively, the ovaries may be surgically removed to reduce the amount of hormone circulating in the body.

Endocrine therapy for breast cancer is usually given for 10 years for most people, depending on the individual risk of cancer recurrence. The two options for endocrine therapy are aromatase inhibitors or tamoxifen.

Aromatase inhibitors – how do they work?

Aromatase inhibitors are a type of endocrine therapy for breast cancer used for post-menopausal women. Post-menopausal may mean that the person has gone through menopause naturally, or as a consequence of chemotherapy, medications to suppress ovarian function or through surgical removal of the ovaries (called oophorectomy). Before menopause, most of the oestrogen in the body is made in the ovaries, so aromatase inhibitors do not work, and tamoxifen is used as an alternative.

Aromatase inhibitors work by lowering the level of oestrogen in the blood by inhibiting the action of the enzyme aromatase, which is involved in producing oestrogen in tissue outside the ovaries (such as breast tissue, muscle and fat). As hormone-sensitive cancers require hormones like oestrogen to grow, having less oestrogen in the body will help to prevent early breast cancer coming back in the future, as well as lower the risk of new breast cancers developing.

What type of aromatase inhibitor should I take?

Three aromatase inhibitors are available for the adjuvant treatment of early breast cancer: letrozole (Femara), anastrozole (Arimidex) and exemestane (Aromasin). They are all equal in terms of effectiveness and have essentially the same side effect profile. All are taken as a tablet once a day. If one aromatase inhibitor is not tolerated, switching may be advised to see if another aromatase inhibitor is better tolerated.

As with all medications, some people experience side effects when taking aromatase inhibitors.

Common side effects of aromatase inhibitors include:

joint stiffness and/or soreness and muscle aches (musculoskeletal symptoms)
hot flushes and/or sweats (vasomotor symptoms)
vaginal dryness and discomfort with intercourse
fluid retention
elevated cholesterol

Uncommon side effects of aromatase inhibitors include:

reduced libido
osteoporosis or low bone density
insomnia
tiredness

If you are troubled by any of these side effects, please make an appointment to discuss your concerns. While some effects may seem minor, when you are taking these medications for many years it is important to address them if possible to ensure that your overall quality of life is as good as it can be.

Tamoxifen – how does it work?

Tamoxifen is a type of endocrine therapy for breast cancer which can be used for both premenopausal and post-menopausal women. In simple terms, tamoxifen works by blocking the oestrogen receptor inside breast cancer cells. This stops oestrogen in the blood from stimulating breast cancer cells so they cannot grow and replicate. Tamoxifen helps to prevent early breast cancer from coming back in the future, as well as lower the risk of new breast cancers developing.

Who should take Tamoxifen?

If you and your doctor are not certain that you have gone through menopause, you may be prescribed tamoxifen initially (eg for two to three years) before switching to an aromatase inhibitor once menopause is confirmed. Tamoxifen is safe to continue for up to ten years, and some women may stay on tamoxifen rather than switching to an aromatase inhibitor depending on their individual circumstances. For women who were premenopausal at diagnosis, and do not become menopausal with other cancer treatments, tamoxifen is the standard treatment.

While tamoxifen does not cause menopause, some of its side effects feel similar to how women feel after menopause.

Common side effects of tamoxifen include:

hot flushes and/or sweats (vasomotor symptoms)
joint stiffness and/or soreness and muscle aches (musculoskeletal symptoms)
vaginal dryness and discomfort with intercourse, vaginal discharge
fluid retention

Uncommon side effects of tamoxifen include:

light-headedness, dizziness, headache
tiredness
rash
nausea
depression or mood swings

Rare side effects:

Blood clots in the veins in the legs (deep venous thrombosis, DVT) or lungs (pulmonary embolus). The risk of a blood clot while taking tamoxifen is about the same as the risk of blood clots for women who take the oral contraceptive pill or hormone replacement therapy. Clots are more common in women who have a family history of blood clots or have an inherited risk of blood clots.
Cancer of the endometrium (lining of the uterus) may develop in less than 1% of women taking tamoxifen for more than 10 years. It is important that you report any abnormal vaginal bleeding or persistent pelvic discomfort to your oncologist.
Eye problems (eg retinopathy or cataracts). Tell your doctor if you notice any visual changes

If you are troubled by any of these side effects, please feel free to make an appointment to discuss them specifically. Whilst some effects may seem minor, when you are taking these medications for many years, it is important to address them if possible, to ensure that your overall quality of life is as good as it can be.

Medication or surgery to suppress ovarian function

Suppressing the function of the ovaries with medication, or removing the ovaries surgically, is another way of lowering oestrogen levels in the blood to prevent the growth and replication of breast cancer cells. This treatment may be recommended for premenopausal women (in combination with tamoxifen or an aromatase inhibitor) to help further reduce the risk of cancer recurrence. It is most helpful for women aged less than 40 at the time of diagnosis of breast cancer but may also help some older premenopausal women with a higher risk of recurrence. It is not necessary for women who have already gone through menopause, because the ovaries naturally stop making oestrogen after menopause.

Ovarian suppression with monthly injections

The ovaries can be turned off temporarily with a medication given by monthly injection called goserelin (Zoladex). This gradually causes the levels of oestrogen to fall, which leads to temporary menopause (and its associated signs and symptoms such as the periods stopping, hot flushes and sweats, sleep disturbance, vaginal dryness and joint stiffness). If goserelin is stopped, then the oestrogen levels return to normal and periods resume. Usually goserelin is prescribed for five years.

Some women will prefer to have their ovaries removed surgically rather than having monthly injections. It is usually recommended to ‘test out’ the experience of menopause first with goserelin for a few months before pursuing surgery which is irreversible.

Removing the ovaries using surgery

Surgical removal of the ovaries is called oophorectomy. This is a permanent way to reduce the levels of oestrogen in the blood. This is usually performed laparoscopically using keyhole surgery which means a faster recovery. Often the fallopian tubes are also removed, and the procedure is then called a salpingo-oophorectomy. As the blood levels of oestrogen fall quickly with oophorectomy, the onset of menopausal symptoms can be faster than occurs with monthly goserelin injections.