Breast cancer is now the leading cancer for women worldwide. There are many breast cancer treatment options available, but which treatment is given depends on many factors. Breast cancer hormone therapy is used when a women has hormone-receptor positive breast cancer. Hormonal therapy for breast cancer includes tamoxifen, a SERM, the aromatase inhibitors, and Faslodex (Fulvestrant).
What Factors Influence the Type of Breast Cancer Treatment?
There are many breast cancer treatment options, with the type of treatment depending on many factors, including:
- the stage of disease,
- whether the cancer has spread or not (metastasised),
- whether the woman has had breast cancer before,
- the age and menopausal status of the patient;
- and whether the tumour is positive for certain receptors, such as HER2/Erb2 or receptors for certain hormones.
Estrogen and Hormone-receptor Positive Breast Cancer (HR-Positive Breast Cancer)
The hormone estrogen is known to stimulate the growth of breast cells via binding to the estrogen receptor. Many studies have also shown the link between increased levels of estrogen and breast cancer, as activation of the estrogen receptor can stimulate growth of both normal and abnormal breast cells. Not all breast cancers express the estrogen receptor, however, but the majority do, with around two thirds of breast cancer patients being diagnosed with hormone-receptor (HR) positive breast cancer.
Age is also a major risk factor for breast cancer, therefore the majority of women who get breast cancer develop the disease following menopause. In addition, the majority of these postmenopausal breast cancers are HR-positive breast cancers. However, HR-positive breast cancer does occur in premenopausal women.
Breast Cancer Hormone Therapy Options
Treatment options for HR-positive breast cancer include hormonal therapies that lower estrogen levels or target the estrogen receptor. These breast cancer treatment options act in different ways to block the signal that estrogen gives the cancer cells to grow and multiply via estrogen receptor.
Available breast cancer hormone therapy options include:
- the Selective Estrogen Receptor Modulator (SERM), tamoxifen, which acts to directly block the estrogen receptor
- the Aromatase Inhibitors (AIs), anastrozole (Arimidex), exemestane (Aromasin) and letrozole (Femara), which act to block the production of estrogen via the aromatase enzyme, which is responsible for conversion of certain hormone precursors to estrogen
- the Estrogren Receptor Down-regulator (ERD) fulvestrant (Faslodex), which acts in a similar way to tamoxifen, by blocking estrogen from binding to the estrogen receptor. ERDs also act to reduce the number of estrogen receptors that are present on the cancer cells as well as alter the shape of the estrogen receptors so that estrogen is unable to bind as well.
Tamoxifen and Aromatase Inhibitors as Breast Cancer Treatment Options
Tamoxifen has been available for more than 30 years as a once-daily oral treatment for HR-positive breast cancer. Tamoxifen was traditionally the main treatment for this type of breast cancer; however, the SERM can cause blood clots, stroke, and endometrial cancer.
Developments in breast cancer treatment options then led to the aromatase inhibitors, which became available in the mid-1990s. Since aromatase inhibitors do not stop the ovaries from producing estrogen, these breast cancer treatments only work in postmenopausal women.
Following numerous clinical trials in different treatment scenarios, the aromatase inhibitors are now approved for a wide number of HR-positive breast cancer indications in postmenopausal women. These studies have shown the once-daily oral treatments to more clinically effective then tamoxifen, with fewer serious side effects. As such, the aromatase inhibitors have gone on to become the "gold standard" for first-line treatment of HR-positive breast cancer in postmenopausal women following surgery for removal of the cancer.
Aromatase inhibitor treatment is not without side effects though. While tamoxifen treatment can cause serious side effects, the aromatase inhibitors are associated with more cardiovascular side effects, bone thinning (osteoporosis) and also broken bones (fractures). In addition, a common side effect of the aromatase inhibitors is joint stiffness or joint pain.
The reason for the difference between the aromatase inhibitors and tamoxifen is the mode of actions for these breast cancer treatment options. Tamoxifen acts by directly blocking the estrogen receptor; however, the estrogen receptor is not confined to breast cells and is present in other body tissues, including the bone, liver and uterus. Since the estrogen receptor has a slightly different structure, tamoxifen can block the estrogen receptor in the breast cells, but also act to stimulate estrogen receptors in these other tissue types. The aromatase inhibitors, however, block the production of estrogen via the aromatase enzyme, without blocking or stimulating the estrogen receptor.
Breast Cancer Hormone Therapy, Fulvestrant (Faslodex)
The third breast cancer treatment option for HR-positive breast cancer is fulvestrant, which first became available in 2002 and is marketed as Faslodex. Unlike, tamoxifen and the aromatase inhibitors, which are once-daily oral therapies, Faslodex is administered by injection once a month.
Faslodex is currently only approved for treatment of postmenopausal advanced (metastatic) HR-positive breast cancer that has stopped responding to other breast cancer hormone therapy, such as tamoxifen. Studies have shown that Faslodex is just as effective, if not more effective, than anastrozole in slowing or stopping the growth breast cancer following tamoxifen therapy in this patient pool. Further studies are underway in order to determine the effectiveness of Faslodex in other breast cancer indications.
Breast cancer treatment options depend on many factors. Patients who are diagnosed with HR-receptor positive breast cancer will most likely receive breast cancer hormone therapy. While tamoxifen was traditionally the gold-standard for treatment of all HR-positive breast cancers, the aromatase inhibitors have now superseded tamoxifen to become mainstay of treatment for HR-positive breast cancer in postmenopausal women with early stage disease, while fulvestrant has shown to be even more superior than the AIs in the treatment of metastatic disease in such patients.
Readers may also be interested in the following articles:
BreastScreen AustraliaBenefits, AIHW Report
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Sources:
BreastCancer.org 2010, "Hormonal Therapy"
National Breast and Ovarian Centre 2009, "Types of Hormonal Therapy"
Christine Redmond - My interest in science and healthcare has seen me working in the laboratory with tiny cells and DNA to helping set up a cancer clinical ...
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