Normal breast cells have estrogen receptors, which allows estrogen to enter a cell to exert its effects. Many breast cancers as well as DCIS also have estrogen receptors There are tests that a pathologist can perform on tissue to detect whether DCIS or cancer cells contain these receptors (known as "estrogen receptor positive"). In these situations, tamoxifen may be recommended.
Tamoxifen is a drug that has been in worldwide use for the treatment of invasive breast cancer for over thirty years. It blocks many of the effects of estrogen on breast tissue, but actually allows estrogen-like effects to occur in other parts of the body. It is used for treatment of metastatic breast cancer as well as treatment of invasive breast cancer that has not spread beyond the breast and adjacent lymph nodes. In this setting, five years of oral tamoxifen treatment reduces the risk of developing metastatic breast cancer and the risk of dying of breast cancer.
Women considering tamoxifen therapy after a diagnosis of DCIS should know the receptor status of their DCIS. If the DCIS is estrogen-receptor negative, then tamoxifen would not be useful.
When tamoxifen treatment is given after lumpectomy and radiation therapy for DCIS, women have an even lower risk of recurrence of either invasive breast cancer or DCIS about half the risk of women who have not been treated with tamoxifen. However, since the risk of recurrence of DCIS is variable, the net benefit for some low-risk women may be very small. This small benefit needs to be weighed against the risks of tamoxifen treatment.
Tamoxifen is an oral medication taken once daily for five years. Most of tamoxifen's side effects can be managed by the woman and her health care team. If you are considering taking tamoxifen, the best specialist to consult is a medical oncologist, because they are the physicians with the most experience in managing the risks of tamoxifen.
Side effects of tamoxifen
Women who have had DCIS should not take hormone replacement
to ease hot flashes, and great caution is advised in taking the over-the-counter
herbal preparations for hot flashes. The issue of hormone replacement
is being intensely studied and women should consult their oncologist and
gynecologist for his/her recommendations in this regard
Risks of tamoxifen
Another potentially serious side effect of tamoxifen is the risk of developing a blood clot. Blood clots may form in the veins of the legs (the most common site because the blood moves very slowly out of the lower legs and is more prone to clot), or, more rarely, blood clots may form in arteries, causing heart attack or stroke. Blood clots in the lower legs can also detach and float through the heart and into the lungs, where they cause a serious complication called pulmonary embolism. All forms of estrogen - from birth control pills to hormone replacement therapy to tamoxifen for breast cancer - carry the risk of these forms of blood clots. This risk is highest in older women, and is thought to be higher in women who have blood vessel changes such as arteriosclerosis that already put them at higher risk for blood vessel events such as strokes and heart attacks.
These harmful events in women taking tamoxifen are uncommon, but because they are potentially very serious, their risk needs to be balanced against the relatively low risk of DCIS recurrence after lumpectomy and radiation. In general, these risks should be assessed for each woman individually, because her other health conditions play an important part in the equation. For example, a woman who has had a hysterectomy (removal of her uterus) in the past does not have to consider the risk of uterine cancer. Women who have already had a blood clot should not consider tamoxifen. Women who are older and have more underlying health problems, especially those predisposing to blood clots, may not want to consider tamoxifen. Women who are younger and wish to preserve their breasts may derive very important benefits for both breasts from taking this drug. Younger women on tamoxifen will need to use a barrier method of contraception (birth control).
Other estrogen-blocking drugs
Aromatase inhibitors are a new class of drugs available to treat breast cancer. Like tamoxifen, they act only on breast cancer cells that have the estrogen receptor. They block the production of estrogen, which in postmenopausal women is dependent on proteins called aromatases. Three drugs - anastrazole, (Arimedex), exemestane (Aromasin) and letrozole (Femara) - are highly effective for postmenopausal women with metastatic cancer or the adjuvant treatment of invasive breast cancer. This class of drugs is currently being studied for DCIS therapy. It is not recommended for premenopausal women, that is, women who are still menstruating. Many physicians presume that because they are so effective in invasive breast cancer that has the estrogen receptor, they may be effective for DCIS when the estrogen receptor is present. Currently, in the absence of research results to show their benefit in this setting, these drugs do not have FDA approval for this use. There appears to be a higher incidence of osteoporosis of the bone with these agents. Increasing calcium intake and weight bearing exercise is recommended.
Women taking aromatase inhibitors should have a bone density study which measures risk of osteoporosis or bone loss. As with other drugs, aromatase inhibitors may cause some side effects. Among the possible side effects are nausea or vomiting, stomach pain, muscle cramps, diarrhea or constipation, dizziness, a general feeling of illness (malaise), weakness and fatigue, hot flashes, loss of appetite, difficulty sleeping (insomnia) and joint pain.