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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 small group of cancer cells group of abnormal 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. Some
of these beneficial effects include, such as lowered protecting against
cardiovascular (heart) disease and lowering 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
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.
Your ovaries will continue to function normally and produce estrogen in the
same or slightly increased amounts.
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:
Uterine cancer - Women in the BCPT who were taking tamoxifen had more
than twice the risk of developing uterine cancer compared to women who took a
placebo (an inactive substance). However, this risk was less or the same as the
risk of uterine cancer in postmenopausal women taking single-agent estrogen
replacement therapy.
Endometrial cancer - Tamoxifen may increase a woman's chances risk of
developing endometrial cancer (cancer of the lining of the uterus). As with
uterine cancer, however, this risk is less or the same as the risk of
postmenopausal similar to that of women taking single-agent estrogen replacement
therapy.
Cataracts - Taking tamoxifen also 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
- 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?
There
is a new class of drugs that is being recommended for use in postmenopausal
patients with advanced breast cancer. The drugs, anastrozole (Arimidex) and
letrozole (Femara), are called aromatase inhibitors (AIs). Aromatase is an
enzyme that helps the body produce estrogen. AIs work in a different way than
tamoxifen. 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 marketed as Evista, reduced the risk of
breast cancer in postmenopausal women by 70 percent. Although the Food and Drug
Administration (FDA) has approved the drug for osteoporosis prevention, it is
not approved for use in connection with breast cancer prevention and is
presently used only in clinical trials.Studies have shown that raloxifene, a
SERM marketed as Evista, reduced the risk of breast cancer in postmenopausal
women by 70 percent. Although the Food and Drug Administration (FDA) has
approved the drug for osteoporosis prevention, it is not approved for use in
connection with breast cancer prevention and is presently used only in clinical
trials.
How does raloxifene compare with tamoxifen in preventing breast cancer?
It
has been suggested that raloxifene, though not as thoroughly researched, is
similar to tamoxifen and may have the same ability. The NSABP, supported by the
NCI, is currently conducting a clinical trial (a study involving people) to see
how the two compare. Known as the Study of Tamoxifen and Raloxifene (STAR), the
study involves more than 400 centers across the United States, Puerto Rico and
Canada. The 5-year study, which started in 1999, plans to enroll 22,000
participants.
Who is eligible to participate in STAR?
Postmenopausal
women who are at increased risk for developing breast cancer and are at least 35
years old can participate in STAR. All women must have an increased risk of
breast cancer equivalent to or greater than that of an average 60- to
64-year-old woman. At that age, about 17 of every 1,000 women are expected to
develop breast cancer within 5 years.
How can I enroll in the STAR trial?
If
you meet the above criteria, you should contact the center nearest you. To
locate the nearest center in the United States (including Puerto Rico) by phone,
call the NCI’s Cancer Information Service at 1–800–4–CANCER (1–800–422–6237).
The number for deaf and hard of hearing callers with TTY equipment is 1–800–332–8615.
In Canada, you can locate participating centers by calling the Canadian
Cancer Society’s Cancer Information Service at 1–888–939–3333.
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