Breast cancer and estrogen

There are many different types of breast cancer, and around 70 per cent of them are sensitive to the female sex hormone estrogen. Cells from these cancers have receptor sites that bind to estrogen, which promotes their growth and spread. These are known as estrogen receptor positive (ER-positive) cancers.

Cells from tumors are tested to see whether they have these receptors. If they do, hormone (or endocrine) therapy may be used as a treatment.

How estrogen affects breast cancer#

Before menopause, the female hormones estrogen and progesterone are produced by the ovaries. After menopause, estrogen is made in body fat, including the fat found in the breast.

Hormone therapy works by lowering the amount of estrogen in the body, or by blocking its ability to attach to breast cancer cells. It may be used to:

• stop estrogen production in the ovaries (before menopause)
• prevent the production of estrogen in fat cells (after menopause)
• prevent estrogen from interacting with tumor cells

This can reduce the chance of breast cancer developing again or spreading.

Breast cancer in postmenopausal women#

Breast cancer before the age of 25 is rare, but the risk of developing it increases with age. Breast cancer is most common in postmenopausal women, and most breast cancers in this group are hormone receptor positive.

As women age, the fat cells in their breasts tend to produce greater amounts of an enzyme called aromatase, which promotes the production of estrogen. As a result, the level of estrogen in the breast tends to rise with age. This locally produced estrogen plays a role in both the development and growth of breast cancer after menopause. Once established, a tumor acts to increase estrogen levels to help it grow, with immune cells appearing to boost estrogen production.

Research has also identified a link between obesity and estrogen production. Data showing that obesity carries a roughly two-fold increased risk of developing breast cancer in older women supports these findings. This makes sense, since women with obesity have more of the fat cells that produce estrogen.

Treatment for ER-positive breast cancer#

Treatments for ER-positive breast cancer may include:

• surgery, such as lumpectomy (removal of the tumor and some surrounding breast tissue) or mastectomy (removal of the entire breast)
• radiotherapy, using precisely targeted x-rays to destroy cancer cells
• chemotherapy, using medication to destroy cancer cells
• hormone (endocrine) therapy, using medication to stop estrogen from helping breast cancer cells to grow

Hormone (endocrine) therapy#

There are several different types of hormone therapy. They may be used before or after breast surgery, after chemotherapy or radiotherapy, in place of surgery (for example, when surgery is not possible because of other health problems), or if breast cancer has spread or returned.

Ovarian suppression therapy#

Ovarian suppression can be an effective treatment for ER-positive breast tumors in women of child-bearing age. It stops the ovaries from making estrogen and is only suitable for women who have not yet reached menopause. It involves either:

• surgical removal of the ovaries (ablation), which leads to a permanent decrease in estrogen production, or
• use of a gonadotropin-releasing hormone, which leads to a temporary decrease in estrogen production

Anti-estrogen hormone therapy#

Anti-estrogen medications are used to block the production or action of estrogen. The most commonly used is tamoxifen. It is often given after surgery and acts to lower the risk of breast cancer returning or spreading to the other breast. Although these therapies can have a number of side effects, for most women the benefits far outweigh the risks.

Side effects of tamoxifen may include:

• hot flushes
• trouble sleeping
• vaginal dryness or discharge
• low mood
• weight gain
• irregular periods
• hair loss
• decreased libido
• skin changes

Aromatase inhibitor therapy#

Aromatase inhibitors (AIs), such as anastrozole and exemestane, prevent aromatase from producing estrogen and so reduce the amount of estrogen within the breast. AIs have been shown to have more benefits and fewer serious side effects than tamoxifen. Newer therapies include medications that cause the breakdown of the estrogen receptor, such as fulvestrant.

Possible side effects of aromatase inhibitors include:

• hot flushes
• joint stiffness
• osteoporosis

Aromatase inhibitors are only given to postmenopausal women. Current research is focusing on newer compounds designed to block estrogen production in the breast only, as the body still needs estrogen for healthy bones, among other things.

Breast cancer and hormone replacement therapy#

Menopause can trigger unpleasant symptoms such as hot flushes and vaginal dryness. Hormone replacement therapy (HRT) eases these symptoms by boosting sex hormone levels. It also reduces the risk of osteoporosis and heart disease.

Because some breast cancers depend on estrogen, women who take HRT for a long time (more than five years) have a slightly increased risk of breast cancer. Women who use HRT for shorter periods (such as two years) have the same risk as women who have not used it. For many women in early post-menopause, the health benefits of HRT may outweigh the risks.

Key points#

• If a tumor has estrogen receptors, hormone (endocrine) therapy may be used as a treatment.
• Breast cancer before the age of 25 is rare, but the risk increases with age.
• Ovarian suppression can be an effective treatment for ER-positive tumors in women of child-bearing age.
• The most commonly used anti-estrogen medication is tamoxifen.
• Tamoxifen is often used after surgery to lower the risk of breast cancer returning or spreading to the other breast.

Where to get help#