News Review From Harvard Medical School -- Longer Tamoxifen Use Cuts Cancer Deaths
Taking a common breast cancer drug longer than usual can further reduce deaths from the disease, a new study says. The research focused on a group of 6,846 women with a type of breast cancer that grows in response to the hormone estrogen. When the study began, they already had taken the drug tamoxifen for 5 years, the standard treatment. Tamoxifen blocks the effects of estrogen on breast cancer. It helps to keep the cancer from returning after surgery. In the study, the women were randomly assigned to stick to standard treatment or to take tamoxifen for another 5 years. By the end of the study, cancer had returned in 25% of women who took the drug for 5 years and 21% of those who took it for 10 years. About 12% of the women who extended tamoxifen treatment died of breast cancer, compared with 15% of the women who stopped after 5 years. The Associated Press wrote about the study December 6. Study results were presented at a breast cancer conference. The journal Lancet also published them online.
By Howard LeWine, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Breast cancer is divided into types based on whether the cells have receptors for the female hormone estrogen. Receptors are proteins on the surface of cells. They attract specific chemicals or hormones, such as estrogen. If the cancer has estrogen receptors, estrogen can stimulate the cells to grow and divide, resulting in more cancer. These cancers are known as ER-positive.
About two-thirds of all breast cancers are ER-positive. The good news is that ER-positive tumors tend to be less aggressive than those that are ER-negative. So the prognosis tends to be quite a bit better. Still, blunting the effects of estrogen is important. It helps to keep cancer from coming back and decrease breast cancer deaths.
Tamoxifen has an excellent track record of improving the outlook for women with ER-positive breast cancer. It blocks estrogen receptors so the hormone can't stimulate cancer cell growth.
Until now, tamoxifen treatment lasted two to five years. The length of time mainly depends upon whether a woman has been through menopause or not.
Women who are past menopause have the option to change from tamoxifen to a different type of anti-estrogen drug after two to three years. This type of drug is called an aromatase inhibitor. It blocks the action of an enzyme that produces estrogen. Examples include anastrozole, exemestane and letrozole.
In women who are past menopause, the effect is to completely wipe out any estrogen in the body since the ovaries have shut down. But that won't happen in women who have not reached menopause. Their ovaries can still make estrogen even when they take aromatase inhibitors.
This study shows a significant benefit to taking tamoxifen for more than five years for all women with ER-positive breast cancer. The treatment continues to decrease the risk of death or a return of breast cancer for many years after the drug is stopped. And tamoxifen is available as a low-cost generic.
The study results are especially great news for women with ER-positive breast cancer who have not reached menopause. Younger women don't have the option of switching to an aromatase inhibitor.
What Changes Can I Make Now?
For women who are past menopause and have ER-positive breast cancer, there are several good options to prevent breast cancer from coming back after surgery. Taking tamoxifen for 10 years is clearly one of them. Based on this study, it may be the best way. But the positive effects of tamoxifen must be balanced against the increased risk of cancer of the uterus and blood clots in the legs and lungs.
Other options for treatment after surgery include:
- Two to three years of tamoxifen followed by two to three years of an aromatase inhibitor
- Five years of an aromatase inhibitor
- Five years of an aromatase inhibitor followed by five years of tamoxifen
There are no studies yet that tell us if any other treatment will prevent a return of breast cancer as well as 10 years of tamoxifen.
For women with ER-positive breast cancer who have not reached menopause, taking tamoxifen for 10 years after surgery appears to be the best option. Until menopause, there is no increased risk of uterine cancer with this drug. The risk of blood clots in the legs and lungs is the same as for older women. Other side effects, such as hot flashes and vaginal dryness, tend to be worse in women before menopause.
There's another option for a women with ER-positive breast cancer who is over 40 but hasn't reached menopause. She can take tamoxifen until menopause and then switch to an aromatase inhibitor. Aromatase inhibitors don't increase the risk of uterine cancer or blood clots.
What Can I Expect Looking to the Future?
The results of this study will change advice right away about how long women with ER-positive breast cancer should take anti-estrogen drugs.
That does not mean that any woman with this particular condition should go back on tamoxifen if she has already completed five years. Nor does it mean that women with troubling side effects from tamoxifen should struggle through another five years of therapy.
Extending tamoxifen therapy will prevent cancer from coming back for some women. But your doctor cannot specifically say that this will be true for you.