What is tamoxifen?
Tamoxifen (Nolvadex®) is a
medication in pill form that has been used for 25 years to treat breast cancer
in women and men. Tamoxifen is one of the most common hormonal therapy drugs. It
has been shown to decrease the chance of recurrence in some early-stage breast
cancers and to prevent the development of cancer in the opposite breast.
Tamoxifen also slows or stops the growth of cancer cells present in the body.
There are an estimated 29 million women at increased risk for
breast cancer in this country, and tamoxifen may offer another alternative to
watchful waiting or prophylactic (preventative) mastectomy.
How does tamoxifen affect breast cancer?
Tamoxifen is classified as a selective estrogen receptor
modulator (SERM) and works as an anti-estrogen: While the hormone estrogen
promotes the growth of breast cancer cells, tamoxifen works by blocking estrogen
from attaching to estrogen receptors on these cells. By blocking the estrogen
receptors, it is believed that the growth of the breast cancer cells will be halted.
Can tamoxifen prevent breast cancer?
In 1998, the National Cancer Institute (NCI) funded a large
research study designed to determine whether tamoxifen would reduce the
incidence of breast cancer in healthy women known to be at high risk. The
National Surgical Adjuvant Breast and Bowel Project (NSABP) conducted the study,
known as the Breast Cancer Prevention Trial (BCPT). The results of the trial
showed a 50 percent reduction in both invasive and non-invasive breast cancer in
the treated women.
Tamoxifen has also been shown to substantially reduce the risk
of developing invasive breast cancer in women who have had ductal carcinoma in
situ (DCIS), DCIS is a group of cancer cells that involve only the lining of a
duct and have not spread to other tissues in the breast.
When is tamoxifen prescribed?
Tamoxifen should be prescribed only for women at high risk for
breast cancer and after a complete medical evaluation of a woman’s individual
risk factors. These risk factors include the woman’s age, personal health
history and family history of breast cancer.
However, tamoxifen may not be suitable for all women at high
risk of developing the disease. An informed discussion between a woman and her
physician is essential in determining the appropriateness of this treatment
option. Women who should definitely not use tamoxifen include pregnant women,
women planning to become pregnant, women with a history of blood clots or stroke
or those who are taking anticoagulants.
How long should a woman take tamoxifen?
The length of time a woman with advanced breast cancer can take
tamoxifen depends on their response to the treatment as well as other factors.
For reducing the risk of developing breast cancer in high-risk women and in
women with DCIS, tamoxifen is generally prescribed for 5 years.
Studies have confirmed that taking adjuvant tamoxifen for 5
years reduces the risk of recurrence of the original breast cancer as well as
the risk of developing a second primary cancer in the other breast. (Adjuvant
treatment is a secondary treatment used to increase the chances of a cure.) The
studies also showed that taking tamoxifen for more than 5 years was not any more
effective than the 5-year treatment.
Does tamoxifen have any other beneficial effects?
Because tamoxifen acts like estrogen in tissue other than breast
tissue, women who take tamoxifen may derive some of the benefits of estrogen
replacement therapy, such as lowered blood cholesterol. Tamoxifen may also
increase bone density, which can slow the development of osteoporosis (bone
loss) and reduce the incidence of bone fractures.
What are some side effects I might experience when taking tamoxifen?
For women, the side effects of tamoxifen are similar to some of
the symptoms of menopause. Two of the most common side effects are hot flashes
and vaginal discharge. The information below does not include all possible side
effects, and not all patients who take tamoxifen will have these symptoms.
Always contact your doctor if you have questions about your personal situation.
Side effects in women may include:
- Hot flashes
- Vaginal discharge
- Vaginal dryness and/or itching
- Irritation of the skin around the vagina
- Irregular menstrual periods
- Headache
- Nausea and/or vomiting
- Skin rash
- Fatigue
- Fluid retention and/or weight gain
Side effects in men may include:
- Headache
- Nausea and/or vomiting
- Skin rash
- Impotence
- Decrease in sexual interest
This list of side effects does not include all possible side
effects, and not all people who take tamoxifen will experience these side
effects. Always contact your doctor if you have questions about your personal situation.
Will taking tamoxifen bring on early onset of menopause?
While some of its side effects are similar to some of the
symptoms of menopause, tamoxifen does not cause a woman to begin menopause. If
you are premenopausal and are taking tamoxifen, you may experience menstrual
irregularities or vaginal bleeding. For some women, there may be an absence of
menstrual cycles. Please discuss your personal health care concerns with your
health care provider.
What are some precautions and recommendations I should know when
taking this medication?
Tamoxifen may affect fertility, so it is important to use some form of birth
control while you are taking this medication. However, do not use oral
contraceptives (the "pill") since they may change the effects of tamoxifen. Tell
your doctor right away if you think you may have become pregnant while taking
this medication.
Take anti-nausea medications only as prescribed by your doctor.
Ask your doctor which over-the-counter medications you can take.
Are there any other concerns I should be aware of while taking tamoxifen?
According to data from large treatment studies as well as the
BCPT, women taking tamoxifen may have a slightly increased risk of developing
blood clots in the lungs or large veins. This may be especially true for women
undergoing chemotherapy (anti-cancer drugs) while taking tamoxifen. Women in the
BCPT also had an increased risk of stroke. Additional risks may include:
Endometrial cancer: Tamoxifen may increase a woman's risk of
developing endometrial cancer (cancer of the lining of the uterus). However,
this risk is the less or the same as the risk of postmenopausal women taking
single-agent estrogen replacement therapy.
Cataracts: Taking tamoxifen appears to put some women at
increased risk for developing cataracts, a clouding of the lens inside the eye.
A few patients have also reported eye problems such as corneal scarring or
retinal changes.
When should I call my doctor?
Call your doctor immediately if you have a fever of 100°
F or higher. You should also call your doctor if you have any questions or
concerns or if you experience any of the following:
- Inability to eat or to drink fluids for 24 hours
- Uncontrolled vomiting
- Blurry vision
- Chest pain
- Shortness of breath
- Calf swelling and/or tenderness
- Vaginal bleeding
- Any other unusual symptoms
Is tamoxifen used as part of chemotherapy for breast cancer?
Studies have shown that a combination of tamoxifen and
chemotherapy drugs after surgery for breast cancer may increase survival rates
for some patients.
Are there other hormonal therapy medications that can prevent breast cancer?
Other drugs are also available for use in postmenopausal
patients with advanced breast cancer. Anastrozole (Arimidex®)
and letrozole (Femara®) are among a different
class of drugs than tamoxifen called aromatase inhibitors (AIs). Aromatase is an
enzyme that helps the body produce estrogen. While tamoxifen blocks estrogen
receptors, AIs block the action of aromatase. Both tamoxifen and AIs are only
effective for treating cancers that use hormones to help the tumors grow.
Clinical trials have shown that AIs delayed progression of
breast cancer longer than tamoxifen in women with advanced disease whose tumors
were hormone sensitive. AIs also show promise as additional therapy for early
breast cancer. Another new drug, exemestane (Aromasin®),
is similar to the AIs but is an aromatase inactivator. Instead of blocking the
aromatase, aromatase inactivators actually destroy the enzyme.
Are there other SERMs that can prevent breast cancer?
Studies have shown that raloxifene, a SERM (selective estrogen
receptor modulator) marketed as Evista®, can
also reduce one’s risk for breast cancer. It was approved by the FDA for the
following very specific indication:
- For the reduction in risk of invasive breast cancer in postmenopausal
women at high risk for invasive breast cancer.
It is important to understand that Evista did NOT receive
approval for treatment of invasive breast cancer, reduction of the risk
of recurrent breast cancer, or reduction of the risk of noninvasive
breast cancer.
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