Endocrine Therapy for Breast Cancer

What is Endocrine Therapy?

Endocrine therapy, also called Hormonal therapy, is used for hormone receptor-positive breast cancer. Endocrine therapy works by ‘starving’ cancer cells of oestrogen that make them grow. 

Hormone therapy is a form of systemic therapy. It is designed to either lower the level of oestrogen in your body or to stop the oestrogen from stimulating the cancer cells. 

The therapy lowers the risk of breast cancer returning or a new breast cancer developing in the treated breast or the other breast.

Who Are Suitable for Hormone Therapy?

Primary hormonal therapy is usually reserved for patients with other significant problems that reduce the options of more radical treatments.

Your doctor will recommend this treatment if your tumour is hormone-sensitive by type. 

Hormonal therapies used to treat breast cancer are not the same as hormone replacement therapy (HRT) used to manage symptoms of menopause.

Endocrine Therapy and Adjuvant Therapies

Endocrine therapy is an adjuvant therapy. 

Adjuvant therapy is treatment after surgery and includes chemotherapy and radiation therapy. The main treatment goal is to help the main treatment be more successful. 

As surgery is the main treatment for many cancers, neoadjuvant cancer therapy is any treatment administered before surgery. It is usually in the form of 

• systemic (drug) therapy, or
• local therapy (radiation).

Who Can Benefit From Hormone Therapy for Cancer?

Hormone Therapy is used for patients with cancer to treat cancer that:

• Has spread too far to be cured by surgery or radiation
• Remains or comes back after treatment with surgery or radiation therapy,
• Needs to shrink before other treatments.

Hormone Therapy may also be used in conjunction with 

• Radiotherapy, 
• Chemotherapy, or
• Other Therapies as an initial treatment 

if a patient is at higher risk of cancer recurrence or if the cancer is outside the local area.

Role of Hormonal Therapy in Breast Cancer

Endocrine therapy is designed to:

• Reduce the size of a tumour before surgery (as neoadjuvant treatment),
• Prevent the recurrence of cancer after surgical resection, and
• Delays or completely stops the growth of cancer cells.

How Does Hormone Therapy work?

The body's hormones can promote cancer growth. Hormone therapy is designed to block cancer-promoting hormones. Hormone Therapy is administered by:

• Injections,
• Tablets, or
• Removing Hormone producing glands (although this is rarely performed these days).

These treatments can cause cancer to shrink in size and keep cancer from spreading. It does not cure cancer.

Types of hormonal therapy for breast cancer

There are different hormone therapies for women who are 

• pre-menopausal 
• post-menopausal 

due to the different levels of oestrogen produced throughout these stages.

Also, therapies differ based on the receptors in cancer. These can be either:

• Oestrogen receptor (ER) or 
• Progesterone receptor (PR) 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.

Anti-oestrogens

Anti-oestrogens work by stopping oestrogen in the body from attaching to cancer cells. One of the most well-known anti-oestrogens is tamoxifen. Tamoxifen can be used to treat women of any age, regardless of whether they have reached menopause. Tamoxifen is taken as a single tablet daily, usually for five years. But, it can be up to 10 years.

Additional rare side effects include increased risks of blood clots, such as deep vein thrombosis (DVT) or pulmonary thrombosis (PE), stroke and uterine cancers.

Aromatase inhibitors

Aromatase inhibitors (AIs) block oestrogen production but only work for post-menopausal women.

Examples of aromatase inhibitors include anastrozole (Arimidex®), letrozole (Femara®) and exemestane (Aromasin®).

Aromatase inhibitors are not suitable for women who:

• Have not yet reached menopause,
• In the middle of menopause, or
• Have temporarily stopped having menstrual periods because of chemotherapy

Aromatase inhibitors are taken as a single tablet daily, usually for five years. But, it can be up to 10 years. If you are being treated with an AI, you may be referred to check your vitamin D level and for bone mineral density (BMD) tests to monitor your bone mineral density levels, particularly if you are at risk of developing osteoporosis.

Side effects of aromatase inhibitors include stiffness and pain in bones or joints (arthralgia) and an increased risk of osteoporosis, which may increase the risk of bone fractures.

Ovarian Suppressions

Ovarian suppressions work by stopping the ovaries from making oestrogen. Drugs like goserelin (Zoladex®), given as a monthly injection, stop the ovaries from making oestrogen temporarily. They only work while the woman is taking the drug.

Drugs that stop the ovaries from working also cause menopause, but this usually only lasts while taking the drugs. However, the effects of these drugs may be permanent if a woman is close to her natural menopause when she starts treatment.

Oestrogen production can be stopped permanently by removing the ovaries surgically (oophorectomy) or giving radiotherapy to the ovaries. Ovarian treatments are only suitable for women who have not yet reached menopause.

Surgery to remove the ovaries or radiotherapy to the ovaries causes permanent menopause. Women who have these treatments can no longer have children naturally.

Progestins

Progestins are artificial forms of the female hormone progesterone. They are sometimes used for women with secondary breast cancer. The most common progestins are megestrol acetate (Megace®) and medroxyprogesterone (Provera®). Progestins are given as a tablet.

Progestins may cause nausea and also increase appetite, which can lead to weight gain. Other possible side effects include muscle cramps and slight vaginal bleeding (spotting).

Everyone is different in how they respond to treatment. If you experience significant side effects with your hormonal therapy, feel free to talk to your GP or oncologists, you may be able to take a different dose or different brand or different medicine.

Do not let side effects stop you from getting the benefits of hormonal therapy.

Ovarian Treatments

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

Temporary Ovarian Treatment

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.

Permanent Ovarian Treatment

Surgical removal of the ovaries, known as oophorectomy, is a permanent way to reduce oestrogen levels. 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.

Possible side effects of Hormone Therapy

All hormonal therapies can cause menopausal symptoms. 

Hormone Therapy for Cancer can cause similar side effects from lower levels of hormones such as testosterone. These side effects can include:

• Hot flashes, which may get better or go away with time,
• Breast tenderness and growth of breast tissue,
• Cardiovascular disease,
• Osteoporosis (bone thinning), can lead to broken bones,
• Anaemia (low red blood cell counts),
• Decreased mental sharpness,
• Loss of muscle mass,
• Weight gain,
• Fatigue,
• Increased cholesterol levels,
• Depression, reduced libido (sex drive) and mood changes, and
• vaginal dryness.

The severity of these symptoms varies between women and between different treatments. These side effects often improve after treatment stops.